FWIW, DK/2 both had reinforcing more or less for free; it did take Imp time, but then you typically didn't have to move bodies at the same time you'd be doing a lot of reinforcing, namely at the start of a dungeon.
More importantly, the whole Keeper's Hand thing meant that you could usually get a particular wall reinforced NOW if need be. Became important in a few levels. Here, the “dispatch creature” command serves a similar purpose, so you should be able to target a wall for reinforcement
Having to pay for Extra Reinforced doesn't seem worthwhile IMO. Stone and Iron are significantly finite resources and I'm not likely to spend them on a wall, or at least not without being able to totally secure a given area. Sealing off the Dwarves might be cost-effective, but with Alpha 6 Imp and trap navigation, I'd probably have to mortgage half my imps in the trap hall. :-/
