Are you running CS3 (CS3 for universal-ness. Speed will increase if you update) apps all together? Or just one at a time?
The question that you have to ask yourself is…
Does your current computer fulfill your needs. Do you feel like you are getting work done, or sitting, waiting for the beach-ball to go away?
Obviously, you have needs for high-end hardware (Final Cut would bring a mac mini to its knees!)
If the answer to the above question says that you are in need of something faster, I recommend a Mac Pro. They are expensive (base price is 2.5 grand!), but fast.
The key to buying computers and not feeling as though you have to keep on buying to stay relevant is future proofing. The maxim here applies: You can go first class, just not often. Buy the best that you can afford, pay for minor updates as you need to, and you can keep a single computer functional for a long time.