in my opinion C-4 is fine the way it is- just wait for more explosives to be added to tpt because from what i've heard Simon isn't to keen on modifying elements, they should put in an explosive with properties like this in the future.
You know, C-4 is a part of the "basic explosives" group of elements. TPT has three such ones: powderish gunpowder (GUN), liquid nitroglycerin (NITR) and, well, solid C-4. Their explosive power is roughly equal, and they differ only in states of matter. I don't think anything should be changed about this. We just need simple elements which explode when being burned, and that's it.