Even if you dive deeper into sound design. There are some refills that pretty much make it absolutely useless for me to try and sample drums, pianos or abbey road sounding keyboards. Like reason pianos, drums, abbey roads, etc.
Synth are always a cool thing to play around with for sound designing. Thor in reason is really awesome. The modulation matrix can be a tad hard to figure out in the beginning though. I still feel like I only grasped a small part of it.
Anyway, check the Reaon refill post out to see what refills I have/bought/got for free.
I pay a couple of hundred every year on refills I'd say. I usually try to find the ones that'll do the same for free, but it's hard to top some of the paid ones.