Hi John,
I'd agree that most of it won't make that much difference as long as you have a good physical connection. I use solid banana plugs at both amplifier and speaker ends (well, my mains and center actually force me to use spades, but I used bananas on my previous speakers, which would accommodate them).
If you want to use wall plates, I think you should be fine as long as you get some of decent quality. Personally, I would probably not use them for the mains, as I like to do a lot of two-channel listening, and I like to keep that path as clean as possible. I don't think that a pair of wall plates will make that much difference, but I have a clean run from amp to speaker, so I just go direct. For center/surround, I'd be fine with wall plates, but those also just happen to be run directly as well.
I've never heard of anyone using a conducting paste of any type, but if you get the right color and market it correctly, you could probably sell it for megabucks to the right guys (I'm thinking $499 for a toothpaste-sized tube)
. I don't think it will make any difference if it's already out there.
The important thing is to use an appropriate-sized cable for the length of your run, and to keep a solid mechanical connection at the terminals.