I have built up some tracks in the past by starting with a small but interesting texture, beat or riff, and gradually growing a song by sequencing a little bit at a time, but these days most of my pieces are piano-centric and I feel that I want to work out this "backbone" before doing accompaniment. Several of the newer pieces are irregular in tempo and I'm still refining them ... so its hard to go to the sequencer now with those (of course, I have a rough take of each, to help the memory in case I don't play it for a few weeks).
Another personal issue is this -- my favorite works in the past have been ones that work fairly well as a solo piano piece (although I have added accompaniment), and I have this mental hang-up that for my current and future songs, I want to be able to walk up to any piano and play them, and have them sound reasonably "complete" without any accompaniment. Of course, this introduces another issue -- I take the solo piano piece to the sequencer and find that I need to thin out the piano part to leave room for the other instruments. "Sometimes, you just can't win."

But you know, the most fun pieces are those that build element by element, usually with some rhythmic structure to keep them going ... the pieces where you capture your ideas ultra-fresh into the sequencer. For example, I started working on a piece this past weekend the good old sequencer way -- a nice melody dropped from the sky while noodling around with a neat synthesizer patch ... do a quick basic bass drum and cross stick beat to ground the rhythm... do a few repetitions of the verse using an acoustic guitar patch ... and start adding different backing elements ... Sunday night, a piano solo appears in crude form ... gee, part of that would make a decent chorus ... let's transpose that and try to insert it ... ya' know what I mean?
Anybody but me interested in this?
Cheers to all, and thanks for listening (reading)

** ncsteff **
Fantom X8 and XR, and too many SRXs
Now if I only had the time ...