as a lurker here for a while now and as someone working with a similar idea on my own site, my thoughts and suggestions would be:
Drummers are a rare internet commodity. I've met tons of singers, guitarists, bassists and keyboard players, but very few people who could not only drum, but record it... so I've been forced to rely on midi drums. Not as good as the real thing by any stretch of the imagination, but still miles better than doing nothing.
Figure out who you still have around that are willing and wanting to do something and figure out what that is. Iron Maiden covers are very cool and you guys do them excellently, but at the end of the day it's a limited field... you could try broadening it... maybe have each participant come up with their dream cover song and have everyone agree to work until all the songs have versions done. Rather than stress on getting them perfectly accurate, concentrate on having fun... that might get people back in the mood to do the more serious task of cloning the maiden songs.
Try to write an original. Have people submit riffs and do the Hetfield/Ulrich thing of pasting them together until you a song. Specify a specific key and then see what kind of riffs you get. It's a very easy way to get the juices flowing.
If it's fun, people will be more apt to do it. That's the primary lesson I've learned.