It really depends on where you are in terms of pvp. Are you capable of getting six paths easily? Being able to place in sage? Serious about Space-time? Let's say you are able to get one event ninja from saving, how much of an impact do you think that one ninja can change and improve your lineup? Depending on your answer, you might need more power and/or get an event ninja to be able to answer questions.

If you don't care about pvp, then go pokemon mode of course and save those coupons.