I’m putting “mixing your own” in the same category in “grinding your own.” If you’re going to go through the trouble of assembling the curry spices yourself (which, granted is not a whole lot of trouble), you might as well go the whole hog and make a really good curry using fresh spices and grinding your own.
To be absolutely perfectly honest, I prefer good spice pastes to anything I’ve made throwing dried pre-ground spices together. Whole coriander and cumin, toasted briefly over a pan, adds such an extra dimension to food. The times I’ve used dried coriander and cumin–who knows when it’s been ground and how long it’s been sitting around–has been worse that just getting out a jar of Patak’s or somesuch.
YMMV.