There are poor gaiters out there and there are good ones, I've worn both and from experience prefer the ones with zips down the front. I too wear long johns on cold days, to me just another form of useful layering, even on a cold day I find it surprising how hot I can get and they are often off and in my rucksack within the hour. I still don't really get a grasp as to why a hiker would not have gaiters to hand, especially when its raining, when walking in wet grass, in mud, and in snow, to me an essential bit of kit. I hate it if I end up having to go into a pub, cafe or restaurant and the inside legs of my walking trousers are covered in mud, I have my standards you know.
Mind you, I always carry a small nail brush with me, that and a small amount of water usually gets rid of the mud easily.
I'm a hiker who no longer wears hiking trousers (I use a rain skirt or a long waterproof coat over my gaiters) but even if I did, the nuisance value of putting them on, taking them off 'X' amount of times in a day would drive me, as it used to, bonkers! The idea of wearing them for hours on end or for a whole day as I sometimes had to is not my idea of fun hiking.