not entirely sure about the smarter part, but hey, i'm here so let's do this bitch. first of all, applying for the new card will mean a hard pull on your credit report, even if you don't get approved.
if you already have the home loan you want and your credit is established and decent, swapping out one credit card for another new one won't ruin you by any means (even for one that's 5 years old). if the annual fee is something stupid like $100 or more, i'd do it, esp if the interest rate is comparable and you carry a balance on the card.
average age of credit history is a relatively minor factor in the grand scheme. as long as you make your payments on time, don't max out your cards, don't default on a loan, and don't have way too much available "credit" (read: debt) in your name, i wouldn't worry too much.