Scott, you're not helping your case much by threatening the company.
I've seen this discussion time and time again in a variety of forums and with a variety of products. While every companies upgrade policy is not exactly like another's, they do seem to follow similar methods. Look at the iPhone forums if you want a good example, and the people upset over there because they have to wait to get the new 3GS don't really have a legitate complaint.
Still, I wonder how much thought went into this particular program and if various scenarios such as yours, Scott, were taken into account. First, we as forum participants have to take you at your word that you spent as much as you say and when it occured. It is possible that you're embellishing a bit to make your case. At any rate, taking you at your word, I would still have to agree that time limits imposed by Webassist are unusally severe resulting in you not getting what you paid for.
While the terms of the purchase are clear at the time of the purchase, it isn't fair. When I saw the new subscription plan, my first thought was "What about the money I already spent?". But clearly in my case, it was money well spent and I got my value from it and then some, because my purchases were no where near as recent as yours.
The most fair implementation of a new upgrade or program that I've seen was at Digidesign. They announce a major upgrade at least 3 months in advance, usually, and invlite anyone to purcahse to current version with a free upgrade. The WA subscription program is a little more involved than that, but I do think they could offer you something for the purcahse you made.
That's my opinion as it's their right to set and enforce their policies as they see fit.