I agree on the 4/5 lug issue. The only viable reason for changing over would be to enable a specific wheel style...and so far, other than finding more of the Lincoln wires or some other wire wheels, I don't see much chance of running across any must-have wheels that I can afford.
It's funny you mention not having a spare. I do have a spare Lincoln wire wheel, and the idea of doing a speedster style rear mounted spare frequently comes to mind.
Attachment 63715
I will be chassis mounting the R&P. Yes, there will be bump steer, but with the correct positioning of the rack and the use of good steering damper(s) it can be minimized. The DIY Unisteer has been the backup plan all along.