Why NOT run an 11-32 cassette @ IMLOU?

Everyone is different of course so what cassette may work for others may not work for you, but my biggest issue would be the one Reece raises re the missing gears.  Look at what gear seems to be your sweet spot, and whether the 11-32 has it.  There will be a few bigger gaps in there.  

I'm usually a proponent of better to have it and not need it than need it and not have it, but there are limits. 

If having the 32, will help you keep your power in line and not spike  power, it is a good thing. More you spike power climbing hills in an IM, the more negative  effect you will have on the run.

How much power you need to get up any hill varies by your weight. Then that is that number compared to your FTP.

Most folks riding in tris ride to hard up hills and to easy down.

IMC I had a 34 that I used a lot climbing those long hills.

Think the same on that last line. With 11 speed being more prevalent nowadays up to a 28t in the back should be fine as far as any gaps go. In the 30's though, see about the gaps, if they're an issue. Someone who can more comfortably pedal over a wider cadence range can get through wider spaced cassettes more easily.

Keep in mind that power does not have to spike when cadence drops on the hills, people choose to do that as a response to slowing down. Though having a gear available to spin more at what they've trained at can help alleviate that desire to push harder.

How much power to carry a given speed up any hill varies by weight. There isn't really so much of a minimum power, not one that people really need to be concerned with. Sometimes just need to deal with it and slow down some more to keep the effort in line. It's a mental trap that many fall into. The extra effort is likely to hurt more than pedaling slower than normal.

If climbing is an issue (and I vary between 185 and 200, and at 190+ it's always an issue for me), you can consider switching to a 50/34 crank  I thought maybe you had one but that was Reece's post.   I have 50/34 on both road and tri, and it makes a substantial difference (acknowledging that's also a $$ difference than just swapping cassettes)