Ok...To start off. I personally change the saddle and pins on all my guitars from the factory plastic to bone. I believe bone saddle/pins/nut do enhance the sound of my guitars and is a fairly low cost/low risk upgrade. (A little bit of MOP inlay on the pins can also give a little bling). Saddle and pins are something anyone can DYI, cutting and installing the nut is probably something for a good guitar tech to do for you and should be under $100
A couple resources for this upgrade, but not limited to, would include:
StewMac Saddles
StewMac Pins
Bob Colosi Custom Saddles and Pins
Frets.com Steel String Guitar Users Manual has lots of info on saddles, pins etc.
As far as strings go here is some basic info:
Quick primer on strings
I personally prefer coated strings such as:
D'Addario EXP Coated 80/20 Bronze Acoustic Guitar Strings
Martin SP Lifespan Phosphor Bronze Coated Acoustic Guitar Strings
While many here love Elixer strings ...I am personally not a fan. YMMV
Coated strings last longer and some will reduce finger squeak a bit. Purists believe the coating reduces tone or some people tend to change strings so often the extra cost for coated strings doesn't make sense.
And for small delicate guitars I love Newtone Heritage Acoustic Guitar Strings
(They are designed to have a reduced and virtually equal tension on each string.)
My general thoughts on string selection.
If you have a guitar that is naturally loud and bright go with Phosphor Bronze strings to bring some extra sweetness and complexity to its sound.
If you have a guitar that is a little on the quiet side or needs a boost in treble use 80/20 strings.
Two properties of strings that have a lot of influence on sound are string gauge and string tension.
Generally the larger the gauge the greater the tension, but not always. A couple websites like Just Strings have some information on string tension for a few of the strings they sell and it can be very interesting. Some manufacturers have the info on their websites. I wish this info was more easily available.
I would say the average steel string guitar player uses what are called "lights". Lights are also called 12's because generally that is the gauge of the high "E"string, but buyer beware that this is not an industry standard and also many sets of "lights or 12's" can have the other strings in the set vary in gauge from brand to brand.
Experimenting with strings is probably the single most effective, easy and inexpensive way to bring out the best tone of your guitar. Trying .11's .12's and mediums .13's can greatly effect the guitars sound. Most modern guitars can handle .13's, but make sure you refer to the guitars manual to be sure before stinging up .13's. (Warning - changing string gauge can change the action of your guitar. For example heavier strings will pull harder causing string height on the fretboard to raise and may require a truss rod adjustment)
80/20, phosphor bronze, coated and uncoated, custom strings sets where the low E A and D strings are heaver gauge to bring out a guitars bass response, etc...etc. The possibilities are endless and the fun of experimenting is Guitar Nerd Heaven!!
Alright ....let's discuss! Agree with me....Disagree with me....