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I know they
say that over at GP but in my experience they get the rest of it right instead. The things Nowi fights don't care about Spd and neither should she.
In a properly supported setup - Dragon Emblem or otherwise - she's going to tank Red units (armed with Swordbreaker in the event those units include Falchions) and punch holes in piles of other non-green low-Res units (especially Armors). These things either will double (Armor) or won't double (Swordies) regardless of Nowi's Spd. And so should Nowi, since she should be holding your QR3 seal.
That kind of invalidates almost everything Spd does, other than preventing her from getting doubled by units she shouldn't be engaging in the first place.
I think it's actually most valuable to take it as her bane and retain all her Atk and bulk.
Sitting on a +Def / -HP myself, really should look through my spare Nowis and see if I can take my own advice...