Yeah, I've now built three Kitty Hawk kits, the Jaguar, MiG 25 and Saab JAS 37 and I have enjoyed them, but you're right, they certainly don't fall together and do take a lot of work. The MiG is probably my favourite, as despite being expensive, over £50 here in the UK, it's huge in1/48th scale!
I think I'd say, if you like the subject, they're worth the effort.
Having said this, their new F-101 Voodoo is supposed to be so bad, I've given it a miss!