Just thought various people's thoughts and approaches to the topic might be interesting to discuss some.
I've noticed that cover bands can take different approaches to keyboards. I think that generally, for the weekender level, keys can be one the more difficult spots to fill but also end up being a spot that the right group can do very well without.
One route is to simply not have or seek to have keyboards and then do some combination of arranging songs to try to cover for lack of keyboards and/or limiting song selections based on instrumentation. If the subject comes up from time to time, arguments against adding keys often involve fewer moving parts meaning less effort for keeping a nice, tight and clean result and fewer mouths to feed means more in each pocket...both valid enough. I've happily played without keyboards.
Another is to have a keyboard player who can also play guitar and possibly other instruments (sax, violin...). I'm currently in a band with type of arrangement. For this band specifically, problems can come from the fact that he's not really a keyboard player who can also play guitar, he's more a guitar player who took piano lessons growing up and has enough connection to the the instrument to help out some. So, it takes care of the arguments above, but depending on the person, can mean some compromises and having the capability but at a lower level than other parts of the group.
And then there's having a dedicated keyboard player, which is the situation in another band. Assuming the skill is there, it's great in doing away with song limitations and arranging for switches. My problem here is that, in my experience, with a lot of rock tunes, this has led to there being keyboards in songs that don't have them in their original versions. A while back, I played with a guy who was real good about this...he had a good attitude about serving the song, so he'd hang back, drop out, do hand percussion when it was called for, and he had a decent overdriven guitar patch where he could throw out some chords to fill-in without being overbearing. That was nice. At the level many people are operating, a big part of playing music is for enjoyment, and sitting out a lot wouldn't be so much fun. But I have to say the result of hearing keyboards in covers where they don't belong bugs the crap out of me (doesn't seem to bother anyone else I play with to anywhere near the same degree). Currently, where that's the case, I'm not in a position to do anything about it except sulk.
So, I've experienced and seen the positives in each type of situation as well as the difficulties and frustrations that can come from each.
