1. [19C+] smart, spirited; thus the spicy n.
2. [mid–late 19C] smart-looking, neat, thus spiciness, attractive looks, neatness.
3. [mid-19C+] (also spiced) sexually provocative; thus spicy on, provocative towards [may have started out as a genuine euph. but invariably carries slightly ludicrous ‘dirty old man’ overtones].
[late 19C] to have a good, if vulgar time.