Whats with the Watts ??

Hi everyone. I'm starting an audio system for the first time and I've been doing my homework -- reading and listening as much as I can. Sorry if I ask some dumb questions along the way...

One aspect I'm very confused over is how much power I need in an amp. So many highly rated amps seem to be in the 50 watt range, yet there are also those in the 100's of watts. My room is about 25 x 15 with a ceiling that slopes from 8 feet at one end to about 18 feet at the other end. The room has 3 walls but opens up into a foyer on one side. I listen to all types of music, but mostly blues, jazz, and some rock. I like to listen at low to medium volumes. Its rare that I would play very loud. If it's important to my question, I seem to prefer the sound of solid state amps.

Being uneducated on the subject, my initial thought is, get more watts. Better to have too much than too little. So my questions are; how many watts should I be looking for and is there something to be gained or lost with too much or too few watts? Thanks.