What if you have the corrupt that increases your walk time?

Maybe it should work not in terms of energy, but consume "1 action" time - just enough energy for every other monster on the level to make a single move (or for the fastest monster to just reach his second move, whichever comes first)?
That would prevent monsters like quicklings from "hit-and-running" you, and allow you to effectively pose at least some fight if your speed has been lowered greatly.

I would like this because of the times I missed the stone circle before figuring it out.

I think quicklings should still be able to hit and run you. Your reactions aren't fast enough to be able to interrupt their movement.

Perhaps don't make it "the same as walk" but pick the lower of the following 2 energy costs:
1) My previous action
2) 1000

Using "my previous action" means we don't have to have the game calculate all the possible things you could have done and find the lowest score (melee? missile? spell? walk? coward walk?)

They would still be able to do that if you do something else (like attacking another monster), since they have several actions to your one. But if you've readied yourself and are waiting for them, you should be able to hit them back first. Whether or not your reactions are "fast enough" would be determined by your To-Hit bonus.

I'm not sure it would make sense... For instance if you're wearing seven league boots, it seems logical to me they would only take effect when actually walking, as boots will not make standing still take less energy.

I don't think that matters. Waiting is not an action. Waiting is a period of inaction. You can take a period of inaction equal to taking a step with or without your magic boots on.

It's rather silly that it's better to sidestep than it is to stand still when you're trying to react to another person.

I agree it feels a bit silly to side-step instead of just waiting. But I don't see why a period of inaction would be quicker with slb than without slb. Unless of course you want the boots to increase your speed, rather than decrease energy cost. That would however take away the slb benefits of traveling through wilderness.
Tricky matter.

I think making waiting take the same amount of time as your base walking time makes sense.

I think you missed my point. You don't 'speed up waiting', you just wait less. The energy cost of wait is somewhat arbitrary in this regard, but if we consider wait to mean 'don't take a step' then it makes perfect sense.