If it's male you could wait til gen 4 for Gallade, as only male Ralts can evolve into Gallade. It'll have the same base stats as Gardevoir but different typing (Fighting + Psychic) and potentially different mvoes as Gallade can learn Psycho Cut but Gardevoir cannot.
If it's female evolve it if you wish but there's no need to power it up until there's a raid that you're actually going to need it in. Sure you have a lot of dust now but since acquiring dust is more difficult than spending it, it makes sense to save your dust and have more than you need than not enough in the future.
There isn't a real need for a second Gardevoir and since yours still has Shadow Ball I'm guessing you don't use it anyway, else you probably would have TM'd it already as either of the other moves are useful for soloing Machamp.
