Add subwoofer to current speakers or upgrade?

I am considering upgrading my speaker system. Currently I have Vandersteen 1B's powered by Classe' CAP-151. I have looked at adding one REL Storm subwoofer to the 1B's or upgrading to the Vandersteen 3A's. I don't think at this time I can go with the Signatures, although I'd like to. The stereo is setup in the basement which is fairly large. I would appreciate any suggestions on this. Thanks in advance for your thoughts. Happy listening!
Unless you listen to organ music (like I do) or movie sound effect stuff, I think it will be better to upgrade to the best Vandersteen can offer--save enough to make this move, and you will never regret. REL Storm is a very good sub, no doubt. Matching speakers with sub seamlessly can be a challenge.
I think the more important question would be the difference between the 1B's and the 3A's at the mid/upper fqz's. While I'm sure the 1B's would sound great with a sub, will they offer as large across the board upgrade that the 3A's would?
I think not, just my opinion though.

IMHO a subwoofer is the last thing I would want to bother with and like the 3A idea, which sogood51 mentions would have the better midrange too.
As someone who has owned every Vandersteen model except the Model 5's (and currently owner of Vandy 3A Sig's and a stereo pair of Vandy 2Wq subs), my personal recommendation is to first upgrade to the Vandy 3A (and eventually the 3A Sig's when your budget allows). To coin a tortured analogy, pairing the 2Wq with 1B's is like putting icing on a cake that is missing a few important ingredients.

The 3A's have very good low frequency response, and substantially better mid- and high-frequency reproduction than the 1B's. Since there are very few recordings with frequencies below 30-32 Hz, the 3A's will do an excellent job of reproducing virtually all music you are likely to hear except for pipe organ.

It is true that the 2Wq subs relieve the main speakers from reproducing frequencies below 80Hz, thereby improving the upper bass and mid-range clarity and transient response of the 3A's. The 2Wq subs are better suited to use with either the 2Ce's or 3A's than the 1B's.

Don't misunderstand my intention here. I am NOT trying to dissuade you from eventually buying the Vandy sub(s) -- they are an outstanding subwoofer at a great price. In terms of "bang for your buck", however, and assembling your system in a logical order, you will be best served by upgrading to the 3A's before acquiring the 2Wq sub(s).