Will I see any benefit from upgrading the springs on my 180sx without upgrading the shocks?

Some but not much...the poorly damped struts will not control the oscillations very well. (causing it to feel very bouncy and uncontrolled)

First off, I must admit Ive never rode in a properly dampened, lowered car before. But, I have after market springs that are decently low (maybe 1 1/2" drop), and the ride isn't uncomfortably bouncy to me. I use cheapish Gabriel shocks. I get about 1 1/2 oscillations before the dampers kick in. I'm guessing with better dampers you would have 1/2 to 3/4 oscillations. I just cant afford shortened Konis which would be ideal. Beware potholes though. Its easy to bottom out and blow out non-shortened shocks.

I did notice quite a difference in the upgrade. My springs are quite stiff however, They were made for a Cavalier, which is quite heavier than my NX. they are ~400lbs rear ~450-500lbs front I think. Dont quote me on that though.

my .02