What do you think about 40 Below's Light Energy Shorty model? Cuts the weight by a third, and if your ski pants have integrated gaiter bottoms (as many do), even deep snow wouldn't get in. Having the full gaiter in the boots seems like overkill on a ski tour.
Also thought about just using a small trash kitchen bag and a rubber band over my ski liner boots, combined with microspikes for traction. Bag will get a little chewed up on a ski tour, so easy to just bring a few.