for the sake of fewer HTTP requests. its not urgent for the site I have in mind since its pretty small yet but for optimization it has got to be good practice. I noticed when looking at the source code that some variables in different files have the same names.
I haven't seen your site but I would assume you could get rid off 1.6.2, 1.6.2.min, 1.7.1, and the 2.0.6.min you are loading here files double and there is no need for it.
Yep you should combine them, but keep in mind the extra bandwidth it might take. If you only need them for a few pages, there is not point having extra stuff download on page that dont need them