I see the author, jskinner, is hanging out on this thread! Have you ever considered open-sourcing SLT? This is your only route to immortalize this amazing piece of software. I'm sure you'd receive immense community contributions and widespread support. If you switch to a donation model + enterprise support plans, I think you're likely to earn greatly more than you currently do. I love SLT and have used it throughout…
I'm curious as to what your evidence to back this statement up is. As is, most donation-ware ends up getting next to nothing in donations.