I'd pick it up, even though I think MM8 is worst in the series. The price that Mega Man 5 for the NES fetches for is pretty close to the price of this collection alone. It seems like a pretty good value, and I'm pretty suprised that the developer cleaned up the bugs reported in a quick amount of time.
Personally, I'm looking forward to the GBA version a little bit more, as the classic GB Mega Man games are colorized. Also, MM 3, 4 and 5 are pretty damn expensive on their own these days, so it makes this (as well as the console collection) a pretty good value.