Add a pair of 2wq's to my Vandersteen 3A Sigs?

There's a pair of Quatros for sale here for about $4300, and given your space limitations maybe if you sell your 3As that could be a possiblity especially considering the cost of the two subs? Ironically someone's also selling a pair of 2wqs for $800 that may be tough to pass up. Best of luck.

Yes. The only thing I might suggest is that with the capabilities of the 3A sigs, a single sub might be all that is needed to get your setup sounding right. You could always add the second one if needed. I've gotten really good performance for years from my single Vandy sub. One of the better pieces of equipment I've ever owned. (Thanks, Richard).

When I owned 3Asigs, I had a pair of 2W subs placed behind and to one side of the mains. They blended so well and so were acoustically "invisible" that I periodically had to check to make sure that they were actually powered up.

Steve, Regarding this lack of punch, is this because of some changes you have made in equipment OR due to any acoustics ? Also Would you know as to which frequency range this is in ?
As am sure you know the "Punch" exists right from 100 Hz and below and if this is in the 50-100 Hz range, it may not be the sub which is a solution.
OTOH a sub is great to fill in and extend the lower end and beyond of the speakers (having run Dual RELs once) although it is quite an effort in getting the position+Phase combination right

And as far as Subs go, the 2WQs are as good as they get from all ive heard and you cannot go wrong with them.