I don't know how one can run out of subjects. I Jugs alone, I've got stuff I want to build that could keep me going for a decade!
But I do kinda get what you're getting at.
One thing I'd suggest - instead of looking at "destination" builds, where you're setting out to build a certain subject, look for a good "journey" build where the subject may not be something you'd normally build, but the kit has an awesome reputation. Building a kit that's just an awesome kit to build, but outside your normal interests, can be an awesome recharge.
Just did this recently with Eduard's 1/144 MiG-21MF dual combo. Far outside my traditional scales and subject areas, but they were an absolute blast and a great way to force myself to hone some techniques to deal with the tininess.
On the Bench: 1/32 Trumpeter P-47 | 1/32 Hasegawa Bf 109G | 1/144 Eduard MiG-21MF x2
On Deck: 1/350 HMS Dreadnought
Blog/Completed Builds: doogsmodels.com