Does anyone think I am waisting my time placing a sheet of plastic between my 2 sheets of 5/8" plywood to help with controlling moisture or would I be creating a problem for the bottom subfloor ?

Yep your creating a problem with dry rot.

Help with what moisture? Deal with the moisture problem directly.

think of a trap/sink,,, houses have to breath, what will happen if you trap the moisture?
now, if you want to completely control the moisture from the crawl space, you can hire a very expensive company that will completely seal the crawl space,, and install a dehumidifer in the crawl space,, only about 10 to 15 grand, depending up size and dehumidifier,,