Add me to the sub list.
So long as your M80s arent clipping or distorting, then extra power isn't going to increase your listening experience noticeably enough to warrant the (likely) extra cost. A sub, on the other hand, can actually alleviate some power issues your amp might be having energizing the lower register in the M80s. Not to mention that, in all likelihood, your sub will probably play flatter, lower than the M80s will and will really round out your sound - especially if 'spolsions are your thing.
