blah blah blah everything about why powermeters are good has already been said.
I have one. I use it and find it very useful for any type of ride I do. Intervals of 20 min or less and longer than 30s and recovery rides are when they are the most useful.
I doubt I'd have upgraded to cat 2 this season without using one.
Powermeters hold their value very well if you buy used. Buy one and use it for 6 months. If you don't like it turn around and sell it.