Less than a $1450 discount for 6 year old speakers with an original price of $3950 seems a little light. You are only $1450 away from new. However, if they are in very good condition I doubt they will "die" anytime soon. If they haven't had anything go wrong with them in their first year of operation its likely they are good to go for some time to come. In any case, repairs on Vandersteens in the USA is a sure thing.

As far as amplification goes you will want quality components upstream from the Vandersteens as they likely will reveal any shortcomings of those components.

I've never owned a pair of Vandies so I don't know what sort of drivers they are or were using. A general rule of thumb is to look at the front baffle to see if the drivers are surrounded by foam or rubber. If foam, they do age over time and become dry rotted. Rubber isn't generally an issue, but look at them carefully anyway.

I would also take a look at the speaker connections to see if they have been stripped from over-tightening or indications of lots of cable changes.

If you can audtion them first, be sure and listen to them in stereo and with just one side playing at a time. If they sound really different when played from left to right, that would concern me. You'd be surprised how many people have one blown driver and don't realize it.

As for the elctronics, that's hard to say without a lot more info on what you need them to be capable of.

There happens to be a pair of Vandersteen 3A Signatures on AudiogoN from a seller in my town and I am going over to listen to them (probably the 6th time I have heard this model). Price is $1900. $2000 would be a good price for a pair in very good condition.

Because of the non-removeable sock grill cloth, you won't be able to see the surround material on the drivers. Whether the surrounds are foam or another material - I don't know - but my Vandies are 21 years old and playing perfectly. They have never needed any service and they just play and sound great.

Foam surrounds can be easily fixed (or DIY!) by any competent speaker repair facility - not a major negative, but you could use it (if you could see them) to bargain with the seller.
I also think ~$2K is a better price. Any more than that is not a good deal. I <3 3A's. But at that price there is a lot of competition. Time to read all the old reviews.