I had a rather
: poor experience in a low price, commercial pure inflatable a few
: weekends ago that leaves me smarting about building an
: inflatable rather than a more rigid one like the Sea Tour.

I, of course, don't know what boat you were using - some inflatables are meant purely for floating down rivers, for instance - but a poor experience in a single design means little when there are so many other designs out there. For what it's worth, the Sonnet users have only good reports for their handling. The Sonnets were designed as sea kayaks, and are fully capable of all that implies.

As for your other concerns, for me, at least, they are overborne by the Sonnet's advantages as a folder. They may not be, for you, of course!
BTW, roof racks are nice, but optional for transporting a rigid kayak. They can be strapped directly to the roof of your car, with some padding in between.

Good luck!