I agree with the idea of a market place for assets (sprites, animations, audio, etc.). I do, however, see a problem with a template market: support.
Say I want a tower defense template, so I pay $10 and get the template. Now I want to make some changes because, being a generic template, it's not exactly what I need. Since I didn't code it, and it can be assumed I don't know how to code it since I had to buy it, will the developer provide the kind of support I need to add features, change logic, etc?
I know many of the developers here offer free help now on the examples and plugins they've made, and I know a lot of them would feel compelled to offer support on something they've sold, but how much and for how long?
If you look at it from the reverse point of view, I'm a developer who made a template that I am selling for $10. But now, since money has been exchanged, I am expected to support that template. Bug fixes are one thing, but what about modifications? How will I be able to work on my own games or create new templates if I am continually being asked to make modifications to my original template?
This is just my opinion, but I can see how that might spiral quickly out of control.