So, given that Railgunner's crit works differently than other characters... what would the Moonglasses do on her? They increase crit damage but reduce crit chance, but with Railgunner, those are the same thing?

I don't actually remember how it works, but if I recall correctly, on Railgunner the downside is that they halve the amount of crit damage you gain from bonus crit chance (like Lens-Maker's Glasses now give 5% crit dmg instead of 10%, Ocular HUD gives 50% instead of 100%, etc.)