It's worth remembering that the PSR arranger keyboards are pretty much home and semi-pro instruments that aren't made to rock the house as much as they are meant to rock the den. However, you mentioned that you used the DSP on the drums and did a little sequencing... have you thought of sampling? Perhaps an outboard sampler would give you the sound of your processed drums without taking up your DSP effects on stage. I don't know what the drums on the PSR550 are like but on the 9000 Pro they are pretty good, plus you have the option to sample, or add dedicated drum expansion cards, and/or assign the drums to specific outputs for outboard processing. Those options are what gives the 9000 Pro it's "pro" designation over the PSR's and even the Tyros. But your least costly upgrade option would have to be a drum machine.

Also, sequencing doesn't always mean pecking out all the drums for an entire song: for most dance music you can easily record a few measures and dupe it for the entire song, then go back and edit breaks and add fills.