I really, really like the Roland expansion boards I own because so many of the patches (to me) are instantly usable. I have the VS, Session, Orchestral, and Hip Hop boards in my XP now, and I've adjusted the panel on the bottom of the synth to be removed in seconds so that I can swap the Vocal and Bass&Drum boards I own in an out as needed when recording. I don't really have a favorite board, but I can say that I like the boards I own better than the many I don't (I've owned the Pop, SSS, 60/70s, Dance; auditioned the World, SFX, Techno, more...).
I'd take a VA synth over the VS expansion board, but it won't work if $200 is all I have to spend. In my poorer days, I'd buy an expansion board, load each patch that I liked to user memory, print a list of the expansion board's waveforms, sell the expansion board (I'd buy it used, so I'd break even), and use the XPs non-exp board internal waveforms to (as best as possible) reproduce the exp bd sounds. Works well for some patches, not so well for others.