Hey (it's you!) Dusty, the smallest-time-investment KAB mod is the fluid tonearm damper, the biggest-bang-for-the-smallest-buck mod is the strobe defeater, and the most-significant-improvement mod is the external power supply. (Full disclosure: FWIW I only have experience with the original linear power supply, not the newer switching model.)
I can't say I'm surprised about the Thiels -- I haven't even attempted to sell mine. A lot of them were sold so there's plenty out there, and it's a pretty long in the tooth model by this point, having been introduced in '92 I believe. I'd figure a pair of Arros should be close to an even trade today price-wise, despite I think being less than half the price when new. But if you like the Thiel sound you might also consider the CS 1.6, which although just a 2-way with smaller driver and cabinet and obviously less bass, I thought was in many ways an improvement over the 2.2 (including that model's trait of being less demanding to drive than most Thiels). It should work better in a smaller room just from an acoustical-integration standpoint, though its footprint (but also its sound) would still be larger than the Arro.
