I've always disliked hexed terrain, ever since first playing Battletech. I certainly like the advantages, but for some reason, the terrain hexes just put me off.
So I once pondered on the possibilities of using a laser projector above the table, projecting a hex grid on top of the terrain. This means you'd get to use your existing terrain, hex sizes could be adjusted to suit your scale/game of choice, and once done playing on hexes, you'd turn off the projector and you're back with standard terrain again.
Heck; you could even switch to squares, for a whole range of other games too!
Honestly though; I've never gone beyond the theory of it. So I have no idea about the feasability or costs of such a setup...