You won't have coins to spend in Trophy Rush if all you're doing is Target Blast. 900 is chump change
Psh! I don't need to play Target Blast anymore, since I've already collected all of the custom moves.
Still, for 900 coins, I can buy at least 4 trophies in the shop that I don't have (with discounts, of course), whereas that's not guaranteed in Trophy Rush. The times where I've played a full round of Trophy Rush, I only came away with 3 new trophies per session, and the other 10 or so were all repeats. Sure, 900 coins may be chump change, but blowing 900 coins and not even getting a handful of new trophies is a chump move.