Foxtrot, I would pay the $10 to have a leak check done. That should tell you where your leak is (if you have one). Then that will also garantee that you won't be paying $55 soon thereafter to add more freon. With freon leaks, they never get better over time. So, while a fresh freon charge will restore the cooling, it will only be for a short period of time.

Now, it is possible that if you run your A/C a lot, the heat generated in using the system can break down the freon and reduce your cooling ability. Doing a complete evacuation and refill will fix this problem

As for the headliner, I have had good luck fixing headliners using 3M adhesive glue. It comes in a spray can. The big problem that you will have is you will need to get a decent size opening so you can spray into the opening and coat all of the surfaces (both on the cloth and the backing). Give it about 30 seconds to let the glue start to get tacky. From there you can work in and reattach the headliner.