oesii,
I know how you feel. You can try a few things to improve the response of the controller.
For the fire buttons:
Open the controller and clean the metal contacts with Alcohol and a Q-tip. Next, take a pair of Needle Nose pliers and gently bend base of the contacts so they are closer together. This will shorten the distance you require to get a response. I believe there is also a spring that you can replace with a higher resistance version. You'll have to take it out and then go to your local electronics or hardware store for the right fit.
For the joystick:
The mushy feel is caused by the springs that are attached to 2 plastic "Y" pieces that are on a pivot point for each axis. When the springs loose their effectiveness, the controller gets mushy. When the "Y" pieces start to bend, the centering "locks" at the bottom of the controller become easier to move out of place.
This is normal for a 20 yr. old controller and you will probably need to use the screw trick or jam something in the slot, like cardboard. I believe these two suggestions were by Voltman3 and NE146.
The only options I found are replacing the springs with stronger versions and straightening out the plastic, which requires it to be heated and remolded, not an easy task if you are inexperienced with old plastic. I have been afraid to try it due to the age of the material.
I hope this helps a little.
- VD