5W is not going to make any difference. Roughly speaking, 100W sounds
twice as loud as 10W.

Amplifiers have not make big leaps and bounds in 10 years, but buying
a good separates one might be worth it. A good dealer will let you
take yours in and compare it along side one of theirs. It's worth it!

It amy also be worth considering buying a multi-channel amp so that
you could go surround sound in the future. It'll cost you more now,
but better than changing again in a couple of years.