I always thought that the Connie refit kinda got shafted since the Excelsior, Miranda, and Oberth classes continued to be used well into the 24th Century.
It could be reasonable to assume that there are a few still in service, but that they've just never had the good fortune to appear on screen with the later hero ships (with the exception of the Wolf 359 Starship graveyard). I believe the USS Republic, the academy training ship that never leaves the Sol system, is a connie. Not sure if it's a refit, though.
Or perhaps Starfleet discontinued the line because Connies were always getting the snot kicked out of them (The Enterprise was crippled pretty much every time she fought in the TMP movies, and the Yorktown had to be scrapped and recommissioned as the Enterprise A after the whale probe), the class had been superceded by the Excelsior class, and the Miranda fulfilled a different role in the fleet, and remained in production.
It seems possible, in addition, that the TMP refit of the Enterprise and the Yorktown (correct me if I'm wrong, but those are the two known connie refits, right?) was made possible by the ease with which the miranda class could be mass produced, and components from that class were retrofitted onto the TOS spaceframe.
Just throwing out ideas here.
I've noticed the popularity of connie models here over the last year. I do think XI has a lot to do with it. I have my own connie overload going on around my desk. There's a TOSserprise hovering over my tower case, a JJprise on the chest of drawers to the right, and a TWOKerprise to my left. And holy hell it's gorgeous.
Anyway, I await further exploration of your design ideas, I like what you've done with the secondary hull - the curved cut-ins on either side of the deflector give it a kind of refined, almost art deco vibe.
