Hi Pete
to the forum! How did you hear about us?
If you're weighing up the option of a 12", I'm guessing you've already factored in the size, weight, portability etc?
If I was going to upgrade from an 8", it would
definitely be to a 12", as long as I could still transport it as required.
I've got a 10" dob (GSO from Bintel), and I've looked through plenty of 8" and 12" versions of them, and the 12" is definitely worth the extra $$$. It will show you more detail on planets (if the seeing is good) thanks to the longer focal length and more light gathering.
I can't
really justify going from a 10 to a 12" at this stage, but would probably more be looking at going to a 15 or 16" truss dob.