To my knowledge, your soundcard only affects the sound being sent by your computer so you can hear it, not the quality of the actual sources of the sound (in this case, Reason's various synths and samplers). I could be wrong, but I believe the answer to your question is no.

Also, Dreq, while I too am a big software user, I find tweaking real knobs to be much easier and more fun than using the mouse. Using the cursor, I might be fast at finding the knobs on the Subtractor, for instance, but my hands are faster.

Don't forget in reason you can record knob by knob, which is extreamly usefull.

And yes, your soundcard only affects the quality of sound YOU hear. After i got my Gigabyte Triton Pro2 board, I was blown away by how much better games sounded with the on-board sound than with my audigy2.