I didn't understand it that way :).
Well, the thing is that I see your approach as equally "structured" as Padrino. If I want to use Vesper Plugins, I have to use Vesper. So your approach - in my eyes - is not "more unstructured", its more "a different kind of structure". As far as I can see it, you don't put a lot of weight into controller/routing-things, but have more emphasis on plugins, which Padrino mostly lacks.
But the fact that you didn't use Padrino and implemented your own structure on top of Sinatra shows that Padrino didn't fit your bill - so my curiosity just springs from the that fact. I always see this as a chance to find new needs and insprirations that Padrino can support and use. So, rant away :).
Aside from the asset-handling problem, bundler can easily support loading plugins from git(hub), as long as they are gems. Why didn't you just settle for that? Then, the only problem that remains is asset handling. There, I am quite in favor of not polluting the main project, but I also don't want to add a asset compilation toolchain just for that :/.