I agree with you concerning the 75, but we don't have a basement and my husband is concerned about the excess weight on the floor (I shut down a 20 long before I told him about the upgrade since it is a legitimate concern), and my main reason for upgrading is because I want the extra height to add some cyps. Then again, I do have a 75 community tank. I just hesitate to convert that to a Lake Tang tank because it's heavily planted and absolutely beautiful.
Anyway, whatever suggestions you may have for the 55 would be much appreciated. So far, cyps are the only species I've decided on (plus my pearly ocellatus). I'm also considering goby cichlids and some julis.