In all honesty, I prefer Mars, the Bringer of War. However, I do agree that for the context of the episode and its dreamlike quality, the far more famous chorale from Jupiter is a good choice. I simply wish they had added more of the rest of the song, which is equal in splendor. However, I do understand why they did not, as the chorale is practically an independent song at this point.
The episode Ice Cream features Tchaikovsky's Waltz of the Flowers, who in all honesty I prefer to Holst, but please, do not mistake preference for disdain. As with all of the greats of the classical period, Holst has a definite and superb place at the head of all music, hand in hand with Tchaikovsky.
I wonder how the plot of an episode that would feature the 1812 Overture would go.