Hi Henry,
to IceInSpace!
Whether it's truss or solid doesn't change what you can see - the 12" versus the 8" is the difference. That's a whole lot more light collecting ability in the 12" which puts more faint stuff within reach. More resolution for planetary/lunar viewing, too.
The difference between the truss style and solid tube is:
1) weight
2) portability
3) setup time
4) Cost
The truss can fold up smaller and is great for portability, as the 12" solid tube is a BIG tube - think HOT WATER HEATER.
The truss will require a little longer to setup and start viewing, but not significantly.
$1700 seems a lot for a 12" truss - you can get a 12" solid tube for under $1000.
Check my
equipment page for what a 12" solid tube looks like - I have mine on a EQ6 mount but I still have the dobsonian mount for it that I still use occassionally.
I hope that helps!