Aluminum bicycle frames age well and don't mind moisture. If you've been riding your aluminum framed bike fairly regularly throughout the years, at your present weight, then yes, you've subjected it to quite a bit of stress. OTOH, if you haven't been riding it that regularly throughout the years and only occasionally, or perhaps, just on the weekends, then you should most probably keep your bike and not sell it.

I've always relished the idea of buying a chromoly steel framed MTB and upgrading the fork and derailleurs to something really over the top.