What is parking like round your way? It can be anything from difficult to impossible round London, which gives a big plus to rehearsal venues that can supply functional equipment. However, unless you are looking at one of the functions of the venue to be demoing gear for sale, cheap, solid and reliable is probably better than splashing out on really expensive gear. Perhaps test the waters by having a small amount of fancier gear available at an increased hire charge?
Also, don't forget to have some spares. Even well looked after gear can go wrong and being locked up with a room full of monkeys night after night is likely to increase the rate of failure! I've turned up to a rehearsal room and found various bits of equipment to be dead; if the studio hadn't been able to swap it round, that could have blown a rehearsal night (and unhappy punters aren't likely to come back if they can find somewhere else).
Final thought - how about also providing some storage space. When I used to rehearse up in Central London, we hired a PA along with bass and guitar amps; the drummer used to keep his kit in a locker at the studio, where he used it with several bands and could also easily pick it up for gigs round the area. It might look like a waste of space but, suitably positioned, could help with soundproofing and may also attract back regular customers and the kind of people who are interested in playing through their own gear and treating other people's stuff with respect.
Wulf