Many of us with SPS dominated tanks use sandbeds, and don't clean them - ever. Granted, there's always some disturbance from a fish like a wrasse or moving some rocks around, so there's some export of detritus.
But detritus under the strict definition of the word doesn't contain any pollutants that cause issues in tanks. By the time it actually makes it to "detritus", all available phosphorus and labile organic carbon has been consumed.
Make your own decision, but there's no harm in keeping a 2-3" sandbed in an SPS tank. If you want proof of this, see Sanjay Joshi's tank
here, and Richard Ross' tank
here. In my own case, I have a 20g nano set up in 2004. The coral population is largely acropora, montipora and small-polyp turbinaria, though there are a few LPS and softies thrown in there as well. It has an approximately 3" sandbed, and there has been no systematic maintenance of it since the tank was setup. And yeah, it grows SPS like mad, to the point where the colonies need to be heavily pruned once every couple of months to prevent flow restrictions and shading.
