I wear only kilts and have done so for quite some time now, and I can say that for my lifestyle I haven't found anything yet that I needed pants for. When I hunt, camp, and fish I wear gaiters and bug spray, what I rock climb I wear bike shorts underneath and have a speacial kilt with a "button hole" in the aprons so I can waer my harness underneath and pass the carbiner through the hole. When I SCUBA dive I do wear a drysuit or a wetsuit so that would be the only time I can think of wear I'm not wearing one.
I think that depending on your lifestyle you will find that switching to full time kilting won't be a large change. You can still do all the things you do, you'll just look classier doing them!