With all the upgrades being to a certain word length it doesn't really seem like a good strategy to ever go for the long words. You have to put a lot of time/effort/risk into long words and the reward is not much better than short ones.
Like, I have 2 upgrades for 1-letter words and 1 upgrade for 4-letter words. I get +48 for "A" or "I", but only +56 for "EONS". Would be more fun/fair if I got like +250-300 for a 4-letter word, and thousands for 8+ letter word.
As it is now, it feels like the best strategy is to just spam 1-letter words as quickly as possible, as it doesn't take any mental power.