I've used DeOxit to clean connections, but mostly on old equipment that was sitting around collecting dust (think....1990's Yamaha amp that has sat in the closet for 20 years).
Worked very well to remove crust and crud, but can't really speak to an improvement in sound.
I've used Stabilant 22 as a contact enhancer in my system. Seems to work well. Not a night/day difference, but is absolutely proven to do what it says it does (The US military and NASA use it, and it is patented, so it obviously works).