Dying Electrical System...Need Help!

I was wondering if someone could offer their expertise...

I've had the same setup in my car for about 4 years now with absolutely no problems. 

Within the last month, I've noticed 3 problems:

1. Headunit shuts compeltely off (screen blacks out), but immediately turns intself back on.  This happens about twice a day.

2. All power to the car dies (I can't start my car).  However, if I lightly tap on the battery's positive terminal, power is restored.  This happens about once a week.

3. Lights dim in-sync with bass notes.

My car's almost at 70K miles.  Is my alternator simply at the end of its life?  My battery was replaced less than a month ago, so it's still pretty good. 

What can I do to resolve my problems?  I've thought about investing in a 1 F capacitor.  I'd really rather not shell out a couple hundred bucks for a high-output alternator if I can get around it.  I've been running a 500W-RMS system through a stock, 60A alternator for about 4 years.