Parades and fairs have always been about excessive use of energy. That we're now considering this stands in tight contention with the meaning of tradition. Is there a correct answer here? I'm not qualified to say.
But Seafair sans Blue Angels isn't ... Seafair. Perhaps, in time, it will evolve, as will we (hopefully taking the national anthem out of sports games), but for now, give the kids -- and maybe some parents -- what they want. 670 tons with how much carbon we're spewing makes a rounding error look significant.
Every sort of event like this has always produced waste; one need not look back further to the amount of literal horse shit from parades mere decades ago.
Pageantry is pageantry. But it means something to people, and to say "we're wasting fuel" -- well, what portion of society doesn't?