I doubt that RV would want or be able to upgrade a pair of older 3s to current spec. Almost every aspect of the 3s has been changed over time as all of RV's speakers are of an evolutionary nature. If he could do it, it would no doubt cost more than simply buying a new pair of 3A Signatures. If you get the chance to listen through the Model 3s that are available and are satisfied with their sound then the price you're talking about seems quite reasonable. Having owned an early pair of 3s, I found their main weakness to be a bright treble leading to a bit of glare in the upper midrange. If you are using "warmer" sounding components it could make for a happy marriage.
Original Vandersteen Model 3
I have a chance to acquire an old Vandy 3 pair for $400-500. I haven't had a chance to listen to them yet. I have a set of Maggie 1.7 with nice electronics, just looking to add a little spice to my life with a box speaker. Looking for opinions on these speakers as compared to applying the same $400-500 to something else in the used market - floor stander or monitor. Would it be worth my time to follow up on these? Thanks