Thanks for the replies, gts and lesterpaul. I went back and was reading through "Mark IIC+ guide for dummies," and found the same info hiding in plain sight. I'm such a dummy!
Spoke with Rich Duvall, Mesa's service manager, yesterday and he let me know a thorough servicing will run $175.00--$275.00, has a turnaround time of three weeks, and that Mike B will be working on it.
I'm still contemplating the C+ mod, but I've never played through either a (healthy) mark iii or the iic+, so I should speak with him about it first and hear what he has to say.
The consensus seems to be that the iic+ lead sound is smoother and more sensitive than the iic, but I can't find a consensus on how the mark iii's sound-perhaps due to the various stripe versions produced-compares with the iic+.