HUDs/overlays are equally fun and challenging for me - and I think they're very fun.
Ultimately, they stand in stark contrast to that which is abstract and are a key part of the idea of minimalism contra maximalism. When you deal with a more abstract piece they're best used as a form of grounding and additional detailing, and I find it best to think of them as added definition to an abstract piece. Look for lines of movement within your work and how you want eyes to flow across the piece as people look at it. Above all else - they have to mean something to be used effectively. Meaning is, of course, in the heart of the artist. :~)