Yeah, that's definitely a concern. From a discoverability perspective, would it make sense to have the smaller number for the blink dogs and the larger number for the floating eyes? That way new players are no less likely to discover this mechanic by accident, but it does takes more effort (or wand charges) to get the other prize.

These fixes decrease effect strength (60->50, 20->15), so they increase the corpses required. Here are the numbers in full:

* ES 100, 2  corpses: 60000 turns (5335  short)
* ES 100, 3  corpses: 90000 turns (24465 spare)
* ES 60,  3  corpses: 54000 turns (11535 short)
* ES 60,  4  corpses: 72000 turns (6465  spare)
* ES 50,  4  corpses: 60000 turns (5335  short)
* ES 50,  5  corpses: 75000 turns (9465  spare)
* ES 20,  10 corpses: 60000 turns (5335  short)
* ES 20,  11 corpses: 66000 turns (465   spare)
* ES 20,  12 corpses: 72000 turns (6465  spare)
* ES 15,  14 corpses: 63000 turns (2335  short)
* ES 15,  15 corpses: 67500 turns (1965  spare)

You don't need to keep all the food down to receive the full benefit of the temporay status - IVAN doesn't model digestive processes, and vomiting only affects nutrition and strength. So, these numbers wouldn't make it impossible or even very difficult to get the TC counter high enough - rather, they would force a player who wants permenent TC to interact with the nutrition mechanics, either by vomiting (sacrificing strength and time), overeating (sacrificing agility and risking unconsciousness from choking), or starving beforehand (which may only mitigate the other two effects).

Yes. Blink dogs and floating eyes both have corpses weighing 30000 grams, which with an effect strength of 100% provides 90000 turns of TC/ESP from 3 corpses (and 60000 from 2, 5335 turns short).

With effect strengths of 60 and 20 you would need to eat 4 floating eyes and 11 blink dogs. Maybe 12 if you're slow. Just sayin'.
As a fix I would suggest strengths of 50 and 15.

You can sell your own severed limbs for 1 or 2 gold, too. Only recommended if you've already replaced it.
If you get a light crystal limb from Silva and manage to detach it, it'll sell for much, much more. Which is just about all a light crystal limb is good for!

Likewise permanent invisibility, which takes fewer wands but sometimes turns out to be undesirable if you want to buy something.

In general I like that temporary states can be made permanent this way because it works the same for every status (even if the means to increase the temporary counter are different), and it's not trivial to accomplish - permanent haste, invis, and even ESP can require cloning/mirroring charges.

Also, I'd agree that the number of turns of telecontrol per gram of blink dog flesh could stand to be reduced. However, getting a blink dog to breed after you've gained permanent invisibility can be really difficult. One time I resorted to throwing various objects at one until it panicked. I think that was enough to get two more.

So for no reason in particular, what locations/situations/moods currently lack an associated music file?

I tried this by editing the script files to remove the levitation flag from an ethereal monster, then polymorphing into that monster.
I could walk through water tiles on the world map with no problem, but I was able trigger and be caught in bear traps.

Yes. But if you can't levitate then you don't want to revert to your true form while you're swimming!

Beowulf fought a bunch of sea monsters, while swimming, in the sea, with a sword. Presumably an IVAN character with nice artificial limbs could do the same. I think an increased strength requirement for all weapons while swimming would make sense.