I wear my line jacket (sometimes) when I work with the band alumni group at my alma mater.
I've got several caps/hats/t-shirts/sweatshirts/etc. that I wear from time to time...
I have paraphernalia on my car (not too much, though - license plate/stickers/etc.). And every now and then, I might buy something new.
Bottom line: I am Greek until I die, so I reserve the right to wear letters/para when and where I please....
However, overkill is bad, whether you are active/undergrad or alumni. Less is more, they say....