I took a Quarterdome T2 plus tent on recent ride across Africa. I camped in it for a majority of the 120 nights. On the positive side, I liked the extra length, overall height of the tent as well as having two doors and vestibules. On the negative side, the nylon zippers stopped working by end of the trip. It wasn't the only tent with that issue and we had a sandstorm one night that contributed, however for longer term reliability I now look at zippers on tents.
Yeah, the regular Quarter Dome T2 runs on the short side at 85" long, but saves a little weight that way. The Plus is extra long for any lightweight tent though.
Most tent zippers will have issues with dirt and dust. I don't know of any that won't. They all eventually stop holding after a while too. It's easily temporarily fixed by clamping the zip pull on either side a little with some pliers to make it tighter. It seems like I do remember hearing about some issues with the fabric at the end of the zipper or door on either the Quarter Dome or Half Dome though, can't remember. I don't think there are better zips than nylon. Metal is too heavy and not any stronger or better in terms of wear from what I understand. I don't think I've seen any made with cheap plastic, but some of the cheaper tents definitely use cheaper, smaller toothed zips.