Oh, man. Guess I'll have to buy a second set of Hasnens at some point. Yikes. I shoulda just stuck with my space-wasting gray plastic Craftsman organizer trays.
You've got a bunch of vintage cars... that means fasteners that are going to be less-than-willing to come apart easily.
Go with 6pts.
HOWEVER... when I was a kid, my friend's dad told us to have two of every tool, so that while we're working on one side of the car, the other can be working on the opposite side without waiting for the tool.
(He raced Fords in NASCAR in the '60s, so they worked on cars a lot)
I've got 6 and 12pt 1/4 drive and 3/8 drive, but for 1/2-inch I've got a full set of 6pt standards and 6pt impacts.
I have one set of deep 1/2-drive sockets, and they're impacts. Both sets of my 3/8-inch deeps are 6pt.
For storage, I've found the the Craftsman plastic rail system to be the best... they take up the least amount of space, and I can quickly grab the whole set and carry it to the car.
For my junkyard box, I've got full sets of 6pt sockets except for the 1/4-drive. I only have one of each size in each drive, but some of them overlap: like 7/16-inch in both 1/2- and 3/8 drive, etc. Plus I have standard and deep in all drives, so when a bunch of us are at the junkyard, we don't have to wait for sockets and pass the tools.
So Bull, in answer to your question... you don't have enough sockets of ANY kind until you've got two of each in your shop box, a full set in a junkyard/road trip box, and a full set for the trunk of each car.
Glad I could help!
-Brad