As with all Thiel products, the first generation breaks ground and the next generation(s) add refinement. I can speak directly to the CS7 which went into production at the end of my tenure. Its primary problem is its concrete baffle - an error in my assessment. Concrete shrinks and eventually cracks, most notably at the sides of the woofer and/or passive radiator. That can be repaired with epoxy. The 7.2 switched to a mineral/polymer casting without the shrinkage problem.
The biggest performance difference is the next-gen drivers in the 7.2. Those years from 1994 to 2000 showed significant progress in motor and diaphram design. The 7.2 tweeter (if memory serves) has 20dB more dynamic range than the 7 tweeter. (Lessons learned developing the CS6 which came after the CS7.) The other drivers also sported enhanced motor shunts and driver geometries that added significant refinement.
Rob says that most of the CS7s were field upgraded to 7.2 drivers and XO tweaks while retaining the CS7 cabinet as-is. Broken baffles were sometimes factory swapped to CS7.2 baffles.
I have a pair of CS7.1s - 7.2 drivers and XOs in a CS7 / concrete baffle cabinet - with cracks that don't bother me. I directly compared the 7 vs 7.2 at Rob's CSS in 2012 and reported that the 7.2 is cleaner / more pristine and dynamic. The CS7 has an 'easier', more laid-back presentation. I'm told the frequency and phase responses are virtually identical. The upgrade is in the faster, more dynamic, more linear driver response of the CS7.2 drivers.
I would suggest that the CS7 should sell for significantly less than the 7.2 on the used market. FYI: there were around 1000 pair of 7s and 2500 pair of 7.2s sold which fits the general pattern of next-gen sales increase ratio.
