You are right, hard top tents are a completely different animal
Some things to consider
Weight - you pay a lot more for less. For example, the difference between a quality fiberglass tent and carbon fiber tent is about 15 pounds, more strength but you pay another $1000. Really hard to make a light fiberglass tent as the shell is really thin, this is what you pay for, everything else can be changed but your shell is your tent.
Fabric - Completely different concept from a folding tent. Since you have less fabric, it has to breathe better. Since the tent is smaller, you need to use the whole tent which means you lean on the fabric and need it to be secure and hold you in like a lee cloth on a sailboat's berth.
Insulation - Water condenses on cold fiberglass so it has to be insulated. The better tents actually have insulation and an air gap in the ceiling, good for cold but also good for heat (you can sleep in). The base has to be insulated or it will suck the heat right out of you.
Mattress - goes along with weight, they are heavy. Has to play well with cold weather so memory foam isn't the best choice. Firmer is better than softer as you can alway put on a nice soft cover. Anti-condensation mats are good, a really nice one that has a bit of flex like a boxspring.
Lift Mechanism - Design choice but for expedition use, the crank system has a lot of merit. It is super strong, so you can store thing on the roof and not have to move them to lift the top. They can also tension the fabric drum tight for high winds. The crank acts like a key and without it, difficult to raise the roof, impossible if you don't know how. Padlocks on roof tents are an invitation.
Ladder - simple is good, I like the two piece ladders that you can take the lock off. Yes, camping in a park, anything will work but in sand and soft it is nice to have a two pieces that slide. The upper part is attached to the tent, you can sink the lower part in the sand to stabilize it.
Reparability - everything has to be easy to repair in the field.
Color - sounds ridiculous but I think important. I like white shells because they reflect light, black tents will cook anything that is closed up inside. The color of the light coming through the tent's fabric is a concern. It sounds strange but a lot of the old expedition tents were blue because the color of the light inside is soothing.
Size - again, a picky thing but I've always felt the folding tents are just that a tent, while the hard shelled tents are more like a sleeping bag. It is a similar concept, you buy what you need that fits you and the conditions you go out in. Your vehicle may change but you don't so it is a thing you can buy for life.
Integration - My pet peeve is weight up on the roof. You want to pack light things high, dense things low. I can feel it if I have more than 120 pounds on the roof and gas cans or tires on the roof really bothers me, yeah now I'm ranting so I'll stop.
I would be interested in your views on why you would want to change to a hard shelled tent? There are a lot of designs and I wouldn't want to comment on that unless I knew what conditions you plan to encounter.
