Further to Helen's comments on toning up instruments.

If you don't play your accoustic guitar (or many other instruments, I imagine) for a month, it will sound kind of dead. One trick I've heard: place your guitar in front of a speaker and play recorded accoustic guitar music. This should help to vibrate the wood and keep it ready for the next time YOU get a chance to play.

Yes, guitars get heaps better, especially in the first two years of playing. They also stabilize a bit. Watch to see how your guitar changes shape over it's first winter before getting it set up with a really low action.

Guitars, like harps, don't tend to age gracefully. There's 125 pounds total of tension at standard tuning on a light guage six string. 185 pounds for medium strings. Easy to handle, except that guitar makers MUST trade off strength for good sound characteristics. Most steel string guitars that I've seen which have been continuously played for over 25 years are starting to sound second rate. Then again, I don't know anyone who baby's their guitar the way a luthier would recommend.

My Yamaha? It's one of the best light string guitars I've heard, bright and loud when I want loud. Though I often whistfully yearn for a nice medium string guitar, I smile every time my Yammy falls over knowing I'd be having a fit if it were a $10,000 Laskin.