It's not hard to make beats on the SP1200 alone. I even make my bass lines inside that beast, playing around with short bass tones. I'm so into using it right now that when I used my beloved 3000 yesterday I thought it sounded boring and weak. And I really love the sound on the 3000 too! But maybe it's just a phase I'm going through. But everything just sound beautiful but ruff gritty and hard knocking on the 1200.
Me and my homie Fredfades makes 1200 beats together all the time. Peep some of them at
http://www.myspace.com/deckfades
Check two of the beats we have done on YouTube too:
http://www.youtube.com/watch?v=cXVOy8mdeLE
http://www.youtube.com/watch?v=hgy1LGEIg6c
These are pretty standard beats, but we have worked one some new stuff that really uses all that sampling time possible. And of course, it's mostly 1-, 2- and 4-bar loops we make, but you can stretch that memory a whole lot, and use very short samples creatively. If you sample synth tones you can do a lot of stuff with them.
If you need that extra time you should get a S950. It's not expensive but it's a top quality sampler. But you probably know that already.