Exchange of Two Minds doesn't give you complete mind reading or anything of the sort. It puts your mind in their body. It's basically a more complicated version of MuCo'ing to look like them. If you want to know what they know, you're going to have to do that with a different effect.
Total 100% mind control (the highest guideline for ReMe) is base 25. Which means the lowest level version you could get that is effective (eye range, concentration duration) is a level 35 spell. 40 gives you sun duration.
If we're talking someone who can reliably pull off Exchange of Two Minds, we're looking at a ReMe casting total of at least 45. The most likely structure for this is an even split of xp between Rego and Mentem, so lets say 22 each.
Someone with a 22 in Rego only needs a 10 in Vim to be able to pull off an arcane tunnel that would turn the above level 35 or even 40 spell from eye duration to AC duration - and furthermore that spell would have the added benefit of being usable with every other spell in the caster's arsenal. So now we have an effective sun-duration total mind control effect at arcane connection range done without vis cost, with a considerably lower botch chance, and from a range far beyond touch (the range of Exchange). It doesn't suffer the limitations of the 'group' target, and it can be achieved ten times within a single diameter, as opposed to taking three hours to cast.
So we end up with an effect that is more potent, that is easier to manage and can be done at essentially infinte range. And if you need to read the target's mind, an eye-range InMe can be cast through the same tunnel - meaning the casting level of that is similarly much lower. Borrowing senses is also not overly difficult, and all this gets done without putting some stranger into your own (or your friend's) body. The only downside? The poor target gets 2 warping points each time you cast.
So long-term infiltration becomes one of the few options, but again this is managed far more safely with a year-duration MuCo effect (a ritual, but a far easier one) and just kidnapping the target and putting him in a cell. You'd have to both kidnap and contain the target for Exchange of Two Minds as well, and you'd also have to take far better care of the target...
So I can't see how Exchange of Two Minds is the ultimate in mind control, nor can I see why anyone would choose it for infiltration. Not to mention the year duration is, again, likely to be deal-cincher on why you wouldn't ever use it.
The only thing it could be potentially cool for is doing Guorna's trick of moving from body to body to stay ahead of death. But again, the year duration is what breaks that one. I can imagine in earlier editions it had 'permanent' duration - making it a viable means of life-prolonging. But without turning it into a 'not-entirely-hermetic' spell and making some house-rules to make it able to be permanent, it's not really useful even for that. This is about the only thing I could envision a magus being willing to spend 11 pawns of vis and a high chance of killing one or both targets on - assuming the duration was longer than one measly year.
The more I look at it, the more I can't see any legitimate value to the spell that can't be done with the exact same arts at a lower level, for cheaper less risk and less problems.