Sefton,
Not sure we can give you any general answers to those questions. The price of entry is definitely lower on the Westerly JF-30-12 model, which is as far as I know pretty much the same guitar as the F-412 although many of the appointments are different.
In truth, TMG's response is the right one... you've gotta' choose the one that sings to you. For me, the Tacoma F-512 was "the one." I literally laughed at the thing (really!) when I first saw it on the store wall. The shiny headstock with that blinding white binding and gold jewelry really was the opposite of my guitar sensibility.
Then I played it.
It took me about four trips back and forth to the store over several months hearing the siren song of that bawdy, sassy, tarty thing ringing in my head to actually believe what my ears were telling me. It's what brought me (back) into the Guild fold. I'd thought Guild was long dead.
Anyway, dread's concerns are valid although I think neck width did vary a bit over the years. The nut width on my F-512 is 1-7/8" which I find to be ideal for fingering a 12er. The thickness of my Guild necks through the ages seem to be fairly consistent. I love the profile. they're not thin, though, like my '80s Taylor.