What makes the I17 stay straight is the fact it uses rubber (silicone?) "knuckles" between the tiller arms and the tiller connector and these connectors keep the boat straight until a certain force is applied. While I agree this is good for the times when you want the boat to "stay straight" (it really only stays fairly straight since whatever helm you have at the time will still be there- ie if you have weather helm the boat will slowly come to weather, etc.) the rest of the time it "numbs" the feeling of the boat (IMO).
One could certainly adapt this "system" to any of a number of other boats including any of the F16's or FX-1 (and I'm sure NACRA will sell you the parts!) In Europe the FX-1 sailors seem to have NO trouble raising/lowering the spis without this (I know, I sailed with/against them this past Summer).
I would ask where do you want to sail and who with?
The Hobie fleets and Isotope fleets were the big ones when I lived in NC (been ~8 years now) so I would check into the Isotope (which we let sail with us as F16's and they are light and made in NC) or FX-1. The Inter is a good boat but it's very heavy compared to an A cat but it's not fragile on the other hand.
Just some thoughts-

Kirt