I would buy SGP without waiting. Indeed I already did!
Yes, we will ALL have to pay again when 3.0 is released. And then again when 4.0 is released.
But in my view that's OK. Think of it as a software subscription. It's less than $10/month, and provides fantastic functionality that gets better every year.
SGP used to be an even better value at $100 one-time cost. But in my opinion it's still a pretty good deal at $100/year.