I haven't read this post for a while so I re-read the entire thing and here I go.....
I would totally do this. Especially if it lowered the price. I think it's only fair.
At the moment I can't really say exactly when I plan to use any rendering services, just that I am in the process of getting myself to the place where I would need these services. Like Vern said I really like having the option but don't need it right now.
This would be more than a good idea. At least it will help explain the basic needs, demands and/or wishes of all concerned parties, I guess. I like this idea a lot.
As far as bartering goes, well for any personal projects I'd be happy to see what I can do (can't make any promises), but for commercial work I can't see this as being done due to copyrights and so on.
Just my 2.43349 cents CAD (equivalent to 2 cents USD, and yes I had to look that up)