Putting $4000 tires on a Cavalier won't make it a racecar.
True, but you would be able to corner 10 to 20mph faster, stop shorter too.
It's a point of diminishing returns, these are Sansui's we're talking about.
I recently upgraded a pair of original Baby Advents, which have very basic crossovers and will certainly never be great speakers. I used Clarity ESA caps, Mills resistors, new boards with point to point wiring, upgraded the chassis wire, added a internal brace, installed new binding posts and plates, replaced the grill cloth and refinished the end caps. I knew that I'd never get the money back out of them, but wanted to hear what they could do. The sound quality improvement was impressive.
Anyway, use good film and foil caps of your choice and budget, but definitely upgrade the resistors as they play a bigger role than I think you realize and they are not expensive.