I'll just give you my experience: I'm in Utah now, just making my way north after spending about 3 weeks in the desert. My 17' Bigfoot
has a straight axle
instead of the 4" drop axle. So about 4" of lift, but I still have the 14" wheels on it.
The biggest issue was driving through empty drainages that crossed the roads I was on. A steep drop then right back up again out of the bottom. On the steepest, I did drag the very front and very back of my camper.
As far as slick rock and rough roads, there was no problem. Anywhere I felt comfortable taking a trailer, it had enough clearance as far as that went. With the little drainages, at first I thought maybe more lift would be nice. But then...really I think I'd rather not take my trailer down those roads. It's pretty rough on them. They get on some steep, scary sideways angles, and get kinda beat up.
If it were me, I would use the trailer with the upgraded axle and larger rims, and take a few runs down south or into the mountains. If you think you actually want to pull that thing down crazier roads than it can get down with those upgrades, then think about the lift. You can always do the lift down the road.
But after this first time in the desert with my new-to-me camper, I think I'll actually be less likely to bring it with me next time. Or I'll plan to leave it somewhere and just take day trips in the truck, or do a couple overnight trips just car camping out of the truck and leave the trailer parked somewhere.