Well, I managed to get a second C2 basic via horse trading, so I'm recapping both. I did the op-amps first and let them play a bit before I did the caps, so I think I can accurately describe the changes. The upgrade to LME49860 ICs is a definite must-have modification. Smoother and quieter across the board with perhaps a bit more bass, although that could be wishful thinking as well. I didn't notice as much of a change with the capacitor replacement as the caps that Kenwood used were TOTL (at the time) ELNAs. The Silmics seem to be slightly smoother than the original caps (could be the fact that they are low-ESR or that could just be a function of replacing 30-year-old caps with brand-new caps). Just make sure when you do this work that you have (a) a good soldering iron with a small tip, (b) lots of soldering braid and (c) a high-quality solder sucker.
While the kit that is sold online uses higher-voltage caps for pretty much the entire recap, that isn't necessary. Get the BOM from the service manual and get the same voltage values, otherwise you'll have issues with space. The second C2 I have has a couple of additional problems that I'm trying to rectify - the busted balance pot (unobtanium) and a channel out in the headphone amplifier. After checking all the connections, I've pretty much narrowed it down to the SIL IC that drives the headphone amp. I'll be installing a DIP8 to SIL8 adapter board with a single LME49860 to replace that as well, but I'm still waiting for the parts to arrive.
While the IC upgrade and recap doesn't magically transmogrify the Basic C2 into an L07-C II, it does take what is already an overachieving preamp and make it even better...for a hell of a lot less than an L07-C II.
-D