Add a Subwoofer to my Vandersteen 1ce s or replace with Revel Concerta2 F36

Being a Vandy fanboy, I am hardly impartial, but I, too, would opt to keep the 1ce's and get a pair of 2w or 2wq's in a perfect world (though you would need a pair of M5-HP crossovers or a pair of fixed crossovers matched to your amp).
REL is a good alternative, so is HSU, and they are very reasonably priced.-maybe a temporary fix until you can get a pair of Vandy subs.
John Rutan of Audioconnection would be a great guy to get honest information regarding the upgrades you are considering. 
PM him, his Agon ID is Audioconnection.
B

Well, I hate to be a stick in the mud, but if you are considering the Vandy 2's, I suggest also looking at the Treo's. I bought ctsooner's pair after owning the 3a sigs. It was a good move. I like the more stylish design as well as the improved performance.
Since you feel you need added bass, perhaps the Quatro's would be a good move. You wouldn't need to add the 2w/2wq subs and their footprint is identical to the Treo's. 
Though I know you have a budget, and spending $4-5K might seem ridiculous, just remember that if you are buying a pair of 2sigs and a pair of subs, you really aren't spending that much less and you will be ahead in terms of upgrading.
Bob

I have bought my 3a sigs and Treo's (actually ctsooner's) used, so I don't see a problem. Actually, I bought all my equipment used either here on Agon or USAudiomart.
If you do buy used Vandy's, it would be better to get the most current model. As pointed out, the 2's have been in production since the 80's. Richard constantly upgraded them, so the latest iteration will be your best bet in terms of sound quality. So, a 2ce or 2ce sig should be what you are looking for. Vandies are pretty well built. Even if you do buy a vintage model, your dealer will be able to have them repaired, usually for not too much money.
I understand your wish to keep local dealers in business, I too, feel guilty when I buy used, but the cost savings are the only way I can afford to buy what I like.-Though I always try to find a way to buy something from them, even though it isn't a big ticket item. I also try to give them as much free recommendations as I can. 
Bob

I have ctsooner's Treo's mated with a pair of 2w subs (not q's).
It is a superlative combination. I don't think I'll be changing them for a while.
Bob

Me, too!