Spring is the best time to re-pot. I've had really good luck with my lillies since I started using plastic dishpans. Since they're such heavy feeders, I put an inch or two of composted chicken poop in the bottom with some lily tabs, followed with a couple inches of unscented cat litter (Hartz pH5), with a layer of sand on top of that. You can't do that with a mesh pot!
I don't have a deep pond, so when it starts really getting cold I trim off all the long-stemmed leaves and put them in storage tubs in an unheated basement (sometimes the water freezes) where they get a little light. Lillies put out little flimsy leaves near the crown of the plant, and these leaves tell the plant when springtime is coming. If I had a deeper pond, I'd probably just trim off all the long-stemmed leaves and put them back until the spring.
This is the first year I have a couple tropical lillies- I will need to treat them differently!