Hey, I just joined the forum today and saw your post. I'm still learning so wouldn't call myself an expert - and I'm more dance/electronic production than soundtrack - but I'm happy to pass on a few ideas to consider when using loops.
I use Ableton, which is great for working with audio, but I think most DAWs have different ways of achieving the same results. I mainly chop loops up to isolate sounds I want to try. Ableton also has a handy clip mode editor where you can automate volume, transposition etc to change the loop. Alternatively I sometimes put the loop in a sampler to trigger different elements using midi. Definitely try and learn midi. There's lots of good tutorials out there. I also sometimes use the sampler 'slice' function, alter the sensitivity and sometimes you can create some interesting variations of the loop, either playing on a midi controller or inputting notes on the piano roll by hand.
Back to using purely audio, I've seen other producers take, for example, a bass loop, chop it up, rearrange it, then pitch certain chunks up or down so you get a different melody/rhythm, but the sound quality is preserved. You wouldn't guess it came from the original loop.
As others have said above I think it's going to be hard to use an original loop (especially in the style you mention) and create a whole new piece of music out of it easily. A combination of using audio and midi and building up layers of instruments I'd say is the way to go.
Hope some of this is helpful.