The amount of rehearsal needed for a band I believe is proportional to the amount of experience of the players, plus what the band is looking to do. If it's an original band that wants to put out a bunch of new songs, then obviously the more time that's put into it, the quicker it's going to get done. If however it's a cover band with all experienced players, or an original band playing pretty much the same 20 songs, then one rehearsal before a show is enough. Often times no rehearsal is enough.
I think I can safely say that the most succesful bands I've been in rehearsed the least, the least succesful rehearsed the most. I wondered about this and realized there are a lot of reasons for that. I think the main reason is the less rehearsed band is more psyched to play then the ones that are beat to death. could be also that there's a lot less time spent "working things out" and getting sick of each other than just being out there playing, moving forward, and having fun. Provided everyone in the band does their homework I think less rehearsal also adds to the excitement of the gigs. Everyone has to be just a little bit more on their toes and in my experience that makes a difference. My worst gigs seem to have come after the most awesome rehearsals where we knew (thought) we were smoking.
And finally... I play in a lot of bands and have taken some crap for saying, "I don't need to rehearse." Sounds like an ego thing, but it's not. It's an experience thing. I've paid lots of dues. From age 15 to about 19 I rehearsed 3 times a week. I've since done the same with a couple of other bands over the years. I've easily played over 1500 gigs, with almost an equal amount of musicians. Do I need to spend 2 days a week in the studio so the drummer can get his parts right? No. The drummer might have to, and if it's worth the investment I'll sometimes do it for the band, but truth is I don't have to. If I did, I'd think I had some sort of problem.
There are exceptions to the above rule (complicated material, super high stake gigs, excellent paying situations where someone in the band needs or wants the extra rehearsal time), but the majority of the time I'm with the rest of the guys in your band. If everyone does their homework and knows their sheeiit, rehearsal time could be put into much more productive stuff. Wrting, recording, booking, promoting, etc. Sleeping and relaxing too.