How Much Power is Enough?

I'm thinking of upgrading my YBA 2 Alpha HC amplifier (70 wpc). I'm currently using PMC OB1 speakers that are fairly inefficient at 87db. I really don't play my system at very loud volumes...and I don't think that I'm stressing my current amplifier...but I'm not sure. I'm looking for an amplifier that will bring about a wide soundstage, tighter bass, and exceptional smooth execution of mirco-detail. Would having more power make much of a difference? ...or should I be looking at a higher quality amplifier and stay with lower power like my current YBA? Some amps I've been considering on the USED market are: Pass XA60 monoblocks (lower power), Pass X150.5, SimAudio Moon W-5....
Would these amplifiers be a good match for my system? Would it be an upgrade from my YBA? Any advice or discussion would be appreciated.

calgarian