The great thing about a 75/90g is that they have the same 48" lighting requirements, but with more space front to back to aquascape. A 55g is just way too constrictive, and it's just as frustrating as something smaller.
With a bigger tank, you'll be able to stack the rocks a few inches off the back glass, which will enable you to reach back there with a scraper or mag float. A 55g just isn't worth it.