Anyone's tried repairing/upgrading original Vandersteen 1 speakers?

You couldn't pay me enough to take one of those, even in perfect condition. But since you want it, what is bad about the woofer? If it rattles or scrapes the voice coil is shot and you need another woofer. Anything else and it could be a new woofer or electronics. It should be pretty easy to test and see if it really is the woofer. If it is, I wouldn't touch it no matter how cheap without first knowing if you can find a replacement.

Carefully space your fingers evenly around the dustcap of the good woofer, push in gently and feel what the travel feels like, it should move easily and you should not feel any rubs.  Now go to the suspect woofer and do the same. If it feels any differently or won't move at all, you have a bad woofer.  If this is not clear, pull the bad woofer, either measure it for impedance or put a battery on it and see of the cone travels with the battery and you should hear the voltage popping sound when you touch wires to the terminals from the battery. If all of that checks good,  put a signal on the raw woofer.  

These most likely had foam surrounds. Could be as simple as new surrounds. I have 2CE and 3As. Son has 2CE Sigs. I really like the sound of all three. Very musical.