The only sticking point for me is the part where you say that bugs in previous versions will be essentially abandoned once you release the new version. Unless it is a significant one of course.
I've always thought that if I buy a product with the understanding that I am also buying future bug fixes and support it should not evaporate once you release a new version. To that end I would like to see SGP in its current form solidified in to a non-beta full release with pretty much all the current bugs fixed. Don't add any more features or substantially change the way things are done. Just get it rock solid. Then anyone who does not want to upgrade, and they are insane not to, they at least have a solid stable SGP that they can use until they decide to upgrade.
Having dealt with Bisque on this same issue I was left with a very sour taste in my mouth after spending so much money on their software with bugs and then my subscription ran out and I still have bugs. So now I don't get daily builds to fix them unless I pay another years subscription.
Having said that, I fully intend to buy the new version of SGP. SGP is a steal at twice the price in my opinion. So anything under $99.00 I feel like I am ripping you off.
Many of my friends have been saying this all along. You are under priced. Heck, I paid more for focusing software that doesn't work near as good as SGP.