Is it less than ideal to spend lots of time and money on makeup/beauty to go on a shidduch date? How does one know if one’s doing too much hishtadlus?

The ideal Jew is "a healthy soul in a healthy body". Just about all of our fore-mothers in the Tanach are described as being physically attractive, so obviously, there is nothing wrong with this and it's even positive. The Vilna Gaon points out that "beauty is vanity" only when it's without awe of God, and that physical attraction is a God-made necessity, and He doesn't make mistakes! Thank Hashem that He has revealed in our generation ways (make-up, clothing etc. not necessarily cosmetic surgery, but that too, in rare cases) that every woman can make herself beautiful, and just like medicine, we must use that Godly revelation to our advantage, regarding important things, like to meet a potential husband. This is exactly the "hishtadlut" (human effort and will) which, when balanced with prayer, emuna and hashgacha (Divine intervention), are precisely what "run the world". Like anything, it's not good to go to overboard extremes, and don't forget that the external attraction is just a preparation for the internal and eternal connection as soul-mates, but that's obvious.