CUC's are not a requirement for a successful reef. I think you will find that I am far from the only one on here that prefers not having them. I have found that the crabs fight a lot, eat snails (or just kill them for their shells), and some will even pick at your corals and fish. They are, after all, opportunistic feeders and not picky about what they get.
I prefer to put the fish in the tank to good use. Not only will they keep the tank clean, but they are fun to watch. I have a 40b and my working fish are a Diamond Watchman Goby and a Lawnmower Blenny.
The Goby does an amazing job cleaning the sand bed. He simply sifts sand through his gills ALL day long. If the sand was not rinsed well at the beginning the tank water will cloud up a bit until all of the fine particles are removed by the skimmer and/or filter socks. Beyond that, they a great fish for almost any tank.
The blenny spends his entire day eating algae off the rocks, glass, pumps, anything algae grows on. They can get somewhat aggressive in their old age (I have never seen much aggression in any of mine), but with proper planning this can be limited.
There are a number of other fish available that can do the job of members of your typical CUC as well. These are just the ones I use in my tank.