I can't help you with too much info re the Carmen other than to say that a couple I knew at the time had one in the early '80s. Fabulous little boat, they sailed her up and down the east coast and across to New Caledonia, Solomons, PNG etc.
Only problem I had with the design was headroom. Other than under the cuddy it was all crawl space for me.
Even so that boat was a real favourite of mine.
Now if I'm correct the Carmen was in fact a Swanson copy of a Herreshoff design but I'm not sure which one.
I'd have thought you might find the Carmen to be a bit cramped after the THIII and that if you were to move up from the TH then you'd go something with a bit more room e.g a Clansman, Duncanson 28, Compass
Great boat though, a boat to fall in love with.
ps - If memory serves me well there were some GRP Carmens built with a longer than normal trunk cabin that extended forward past the mast. I've never been on board one of these but I'd guess they'd have a lot more usable space down below. Not as pretty as the flush decker though.
pps- my sentimental feeling for the Carmen may be in part due to the fact that I was absolutely besotted by the female half of that boat's crew. Unrequited though my 'besottlement' was. Ah me.....such it is.