We have a 2007 2350 with thermal windows, and we have no discoloration yet.
There is a lot of glass on two sides against our bed, so the thermals are welcomed there. They keep the bedroom warmer in high-altitude and Canadian camping when summer nights can sometimes get near freezing. And they help some to keep the bedroom more quiet too. If you are ordering a 2350 or 2351 and want to keep your costs down, consider requesting just the two bedroom windows be thermal. I would think Earl could work a price to determine if it's worth doing just the two, or just get all 6 house windows thermal.
Like Keelhauler and ragoodsp say, if you don't camp in places where the night temps can drop way down, you would do fine without them in a 2350/2351.