For a fairly good idea on whether a purchased upgrade will be available, you can look at the flights available to buy, and see if they show a 'MVP Gold Upgrade' icon next to it... that seems to mean 'open 1st seats available' for that flight. As a CO elite, I've been allowed to board early on AS flights, but I don't believe they will upgrade you for free.

No idea about lounges, I'm happy sitting with the poor folks around the gates.