It's a perfectly good idea for a dungeon game. The statues essentially become "checkpoint" goals found in many adventures or video games, but presumably they could be found and attacked in any order, for non-linear, exploration-based play.
I'd also suggest making each statue encounter unique: each in a different sort of location, guarded by different defenders or traps. Statue ideas:
- Small statue that's easily destroyed but very well guarded
- Cleverly hidden statue
- Obvious but very inaccessible statue
- Massive statue (need to call in those rules for shifting/moving things, and Forced Entry skill)
- Super massive statue (need some other clever idea for destroying it, or use time-consuming cleansing)
- Statue carried about by defenders
- Statue running around on its own
And so on. Also: Make good use of that idea of the statues powering a demon lord. That is, make the demon lord an unbeatable boss - but each statue destroyed weakens his powers. The more statues the PCs can destroy, the better their chance of defeating him. But the boss won't be idly doing nothing while the PCs go about this business . . .