Aside from all of the guilt laden pseudo psychological crap replies, the simple question is whether the tobacco will be worth the money asked. You won't know until you pop the top. What does $80 mean to you. If it means a lot then you might want to consider spending it somewhere else.
A 30+ year old tin is a roll of the dice. Some tobaccos age well, other don't. Even if the tin is solid, the contents may not have been of the highest quality to begin with. If the memory of your grandfather smoking this mixture has a lot of meaning and value to you then make your decision based on that, whether or not you open the can.
All this poop about insulting his memory is just that, poop. What you grandfather would think of you spending extra money is an unknown. He might be impressed that you're successful enough to have a bit of fun money. He might not. He might not care one way or another as he's passed on. You could hold a seance to find out.
To me, spending $80 on something that gives me pleasure or has personal value is not a lot of money. I can spend that on dinner for two, and 12 hours later it's on its way to the sewage processing plant. Spending it on something that offers longer enjoyment or personal satisfaction seems a good move.
