When I have ideas I don't like I usually bounce them to audio and then resample them for a new project, I just treat it like any other song I'm trying to sample from. I don't like recycling individual elements because it kind of traps me in thinking about it in the same way as the original idea but I'm sure that could work for other people.
This is a pretty cool idea! I usually just revisit my old projects when I'm feeling uninspired. It's amazing what time will do to the ear.
If i make a good chord progression but its stuck in an eight bar loop, I usually just save the midi to a folder and now I have my own midi sample pack folder