Thanks for the history lesson. I've owned an Epi Casino for 20 years and Gibson semi for 10, and this fact had never occurred to me. What you say is true for the electrics and to a lesser extent for the standard acoustics. It is not true of your Masterbilt, since they were typically designed as their own thing and not as not a replica of any existing Gibsons. It's only now that we're seeing Masterbilts which are really comparable with the cheaper Gibsons in terms of design. For what it's worth, people here can also tell you that Gibson-built Epi acoustics never really matched Gibson acoustics in the way that the Epi electrics did. Casinos were cheaper ES 330s, but Texans were not just cheaper J45s, and Frontiers were not just cheaper Hummingbirds. Scale-length differences again. Before you lecture us on the difference between Epis and Gibsons do a bit more research and get your facts straight.
Yes there are many such comparisons. I'm surprised you haven't found a satisfactory answer among them. But clearly they're not really up to much.
Yes you can compare any guitar you like to any other guitar. You can compare a Squier Tele to a Gibson LP. You can compare a ukelele to a Jackson Soloist. But the things you can compare will vary according to what the instruments you are comparing have in common. Comparing a Squier Tele to a Gibson LP will tell you more about whether you like Teles or LPs than it will about their different quality levels. It might also tell you whether you prefer a bolt-on or glued-in neck, and whether you prefer poly or nitro finishes. It won't really tell you whether the Gibson's nitro finish is of better quality than the Squier's poly finish.
Comparing a long-scale Masterbilt acoustic to a short-scale Gibson J15 is like comparing an Epi Blueshawk to a Gibson Les Paul Studio. The first has the typical Fender scale-length and the other has the typical Gibson scale-length. The first has a poly finish and the second has a nitro finish. Again, the comparison will tell you whether you prefer a longer or shorter scale-length, and whether you prefer poly or nitro. It won't tell you whether the poly or nitro finish is of better quality. It will tell you whether you prefer the sound of a semi-hollow guitar with higher string tension and through-body stringing, or the sound of a solid body with a tune-o-matic/stopbar arrangment and lower string tension. It won't tell you which sound is of better quality, whether it is worth forking out for a Gibson Blueshawk instead of the Epi.
Nobody on this thread has tried simply to fob you off with that line, even if they have used it. People here are genuinely willing to discuss and advise. There is a lot of knowledge here. But you haven't laid out your criteria for assessing quality at all.
I wouldn't like to misrepresent anybody here, but if you read around the board, you'll note that there are people here with vastly different approaches to assessing the quality of guitars. Victory Pete likes the sound of his Gibsons, but when he talks about quality he focuses more on build and finishing issues. So he is critical of the quality of many Gibsons because they have excess glue visible at the joints, some poorly fitting braces and kerfing, and untapered bridge pin holes. If you also care about such details, then the answer to your opening question might simply be, no, Gibsons aren't worth the extra money.
Buc McMaster, on the other hand, couldn't care less about those details, and judges the quality of Gibson on their feel and sound. If you judge quality in the same way as Buc, then a Gibson probably is worth the additional outlay. Bear in mind, though, that Buc also accepts that no Gibson will come to him with the perfect set-up for his needs. If a perfect set-up out of the box is part of what defines quality for you, then again, no a Gibson might not be worth the extra cash. But if you can adjust to a reasonable factory set-up, or are happy to pay a technician to fine-tune things, then maybe it would be.
Several of us have tried politely to find out what your preferences are, so that we can give targeted advice, and you've responded aggressively. For example, I asked very clearly whether you liked the tone of a J15, and you've not actually answered that question. If you'd really done your research you could have replied straightforwardly to that question, and probably explained what you like about it. No need to try every guitar in a shop, of course, but proper research might involve comparing videos of different models to find out which are in the running. A J15 might well be better made than a Masterbilt, but if you don't like the thumping bass, strong mids and less pronounced trebles of a short-scale Gibson the quality issue is meaningless. We'd be better off pointing you to a second-hand Gibson Advanced Jumbo, a Martin or a Taylor in a similar price range.
As I said, there is a lot of actual experience with Gibson guitars here, even if it is not always with the lower-end models. When I bought my Gibson acoustic, it was the least expensive short-scale slope-shouldered Jumbo in the range. It was absolutely worth paying more for than any Masterbilt, because no short-scale, slope-shoulder Masterbilts were available. The guitar's dimensions are absolutely key to its sound, and that sound is the difference between an also-ran acoustic and a guitar I really want to play. So if on the basis of recordings you really like the sound of short-scale Gibson Jumbos, then yes it probably is worth playing more, unless you find that the new generation of more similar Masterbilts is better than the one you own. The release of the AJ45ME alters the picture and makes it harder to answer your question - especially because I've not been able to track down an AJ45ME to try out.
That statement is fairly clear evidence that you haven't done much research yet. Can you imagine the response that an acoustic guitarist would get if he went into the Les Paul forum and said: 'Dude... obviously Squier Teles, Epiphone Dots and Gibson Historic LPs are somewhat different. They're still all electrics'? You came here looking for experience and knowledge and dropped that one?
I'd venture that the 'They're still all acoustics' line suggests that he hasn't played many Gibson acoustics.
Further evidence that you've not done much research on acoustics, AJ. RCT knows his Gibson acoustic history well. It should be added that Bozeman-made Gibson acoustics are not overbuilt, which is why they are considered a vast improvement on Norlin-era instruments. But if your idea of quality is solid build and durability, then you ought to check out some 1970s Gibson acoustics with double top bracing and volutes. They will seem a bargain next to new J15s. They'll most likely sound like a a pile of crap, but their quality in terms of build strength will be unquestionable.
There are more old Martins in the looking good and selling expensive category. Received wisdom is that Martin owners looked after their (more expensive) instruments better. If the Gibsons you see have been are pre-Norlin, they are exceptionally well looked after. If they are Norlin-era guitars, they are overbuilt tanks which most likely sound like crap.
We're not overthinking it. We know you know it's subjective. We just also know that there are a number of classic Gibson models which are radically different from each other. And we also know that there is difference within the Masterbilt range. Whereas you pretty well said that they're all just acoustics. We're trying to narrow things down a bit, and we tend to start from what people like, so that we can try to make our opinions as relevant to the question as possible.