Good ideas, all of them! I would like an accurate single seat replica though, especially of those Alfas from the WWII period. Blown straight eight, man, those really sounded cool on the Victory by Design program.
My favorite replicas are the ones you can really "do". That is, you can get all the bits if you like and make it a very accurate replica. The GT40 is perfect for this, obviously, as is the XJ13 - you can a proper engine, gearbox, etc. and do a very good copy that can outperform the original if you'd like.
Some replicas, like the 917, I really like but the one thing that prevents me from being seriously attracted to them is that flat 12 motor that is almost unattainable. Best I can figure would be to join two flat sixes, and that would cost a fortune. I like the cars, but something is missing.
These Grad Prix racers I speak of would be hard to do for engine. The F cars would be neigh about impossible, but one could use some available straight eights to do an Alfa. It'd be a real shame to stuff a, the horror, Chevy V8 into one of these things like 99% of kit/replica/rods on the streets these days.