Funny you should mention layers. (and more layers) Fran and I discovered long ago that the more layers you add, the more it turns into a FARFISA ... not that that's a bad thing, but you start to loose the individual integrity of each voice, and they combine to make a brand new (organish) entity. Some like that sound. Even I like the mega timbre of a theatre organ, but not for what I usually do. I like a more stripped down tonality ... like I was playing in my favorite band. Good solid bass player, Ringo on drums (not flashy), tasty keyboard comps, with string, choir, organ layers when needed, and a funky rhythm guitarist. Add a tight horn section, and I'm in heaven.
An arranger keyboard puts all those elements at my fingertips.