If you find some good uses in this card then you can try contacting the EO and see if they are able to increase the limit. There have been numerous success stories on this route. The normal CSRs sometimes are unwilling to figure out the truth, or just don't want to dig deep to help.

Otherwise, you can simply dump them and there is no need to keep it open. You still need to monitor it for fraud charges, so think about the hassle to login to an account you never use just for that. Closing the card will not affect AAoA immediately, as closed accounts are still factored into. Right at the closure only your available credit gets decreased, but that is not too much of a problem, since it's only $750. The closed account falls off from report after 10 years, which will lower AAoA, but by that time your AAoA should already be very strong.