The active exhaust is garbage, but everthing I've read, including first hand accounts and mitsu reports, indicates that the rear spoiler does increase downforce when it's tilted.
And yes 180 is reasonable with the right mods. I clocked a max speed of 169.6 on my stealth via GPS with the same basic mods as Swanny.
There's defintely a lot of gadgets in a 3S. Why do you think they're so heavy?
I've recently realized that I enjoy driving my 1G DSM with a 16G on the street and to work a lot more then my Stealth. And I think the reason is that a 3S doesn't feel like it's fast until you're doing triple digits (which I don't really hit in rush hour). The 3S just isolates you from the road so much better and you have a lot more confidence in the handling, it makes it a boring street car unless you're foolish enough to constantly run at twice the speed limit.
On the other hand 80mph in my 1G feels fast (a lot has to do with the crappy tires and worn out suspension). The 16G is laggy (comparitively) and hits all at once, where the small little turbos in the stealth and the extra torque make power delivery a lot smoother and less noticable then being thrown back when the 16G hits. Plus the weight difference is really noticable when driving the two back to back.