RE:If I had $500...what sw rod should I buy?
I would also recommend test driving a few before plunking down the cash. That said, here is my opinion.
If I was getting an 8wt then I would seriously think about a 3pc rod. You never know when you might want to expand your fishing by heading for some bonefish. Avoid traveling hassles and keep it with you while you fly. A 9wt 3pc would also be nice, but you'd probably be using it primarily in the northeast and compactness isn't as high of a concern.
For rods I'd check out the RPLXi, I have mentioned before that it was hard to wipe the smile off my face after test casting it. A buddy of mine has the St. Croix Legend Ultra 8wt and likes it very much. Another friend just built a 3pc that looks to be pretty sweet. The bonus is they can drop a new Redington reel and striper line for the cost of a SAGE 3pc. or a T&T Vector.
I loved the Diamondback Backwater and built one in a 3pc. 8wt. It is sweet, but perhaps a little stiff for some.