Being able to stand up is critical for me. One way to determine this for each individual, is to create a space where they need to sit or hunch over in their current living space, and use that for dressing in the morning, cleaning themselves, and other daily tasks they would do in the van. Do that for a few days or a week and see what issues surface and if that would be acceptable over the long haul. Nothing like practical real world testing to answer those questions.
For me, I knew I didn’t wan to spent that much time hunched over, sitting for some tasks, or kneeling on the floor. Being able to stand up, stretch, etc, is a basic function I don’t want to do without. For those times when the weather is bad, it would be depressing for me not to be able to stand up for a couple days on end.
If you are spending most of your time outside in private location, can shower and dress outside, and most of your activities are outside, it probably wouldn’t be a big deal. If you are stealth camping where you need to do those functions inside the van, it could be an issue, and I would think the height would be of much more concern. There are vehicles that allow the higher height without loosing too much of the stealth ability, such as handicap vans, sprinter vans, etc.
I would always take the height even if loosing some stealth ability.