Regalia are also used in final limit breaks (along with other mats needed). So if you haven't settled on a soul for a given element team, consider saving regalia for those. The number of regalia needed varies; 20 to FLB a draconic eye exchange weapon, 15 for a SSR kamihime weapon, and 10 for union event/advent SSRs.
Although in wind's case, there won't be a wind advent SSR with a FLB for another year at least (ie, no Garuda 2nd reprint on DMM yet). And union event weapon-wise, it's just the pride sword from Lust rounds 1 & 2 until next year.

Just in general, don't expend your regalia willy-nilly. Spend them on something you know you'll use.