I would take "However nice this dress is" as a concessive clause. So it requires a context in which a concession might be made.
A concessive clause might stand alone in a passage of dialogue, where context provided its completion:
"So you're saying you would never spend $500 on a dress?"
"No, never."
"However nice it was?"
"However nice it was."
i.e. "however nice it was(, you would never spend $500 on a dress)?".
But I'm not sure it's possible to find a context for an exclamatory version; except in the case of direct quotation.
MrP