It's a shame someone cut out a piece of that old letter. It'd probably be worth more if it was completely intact!
Seriously though, I wonder if I have any old letters laying around. I think I still have one or 2 from Nintendo. I may have one that I got where I was allowed to send in Champions Forever in exchange for another game(chose Monster Lair, I forget what others were on the list) due to them not mentioning on the retail box that it required the Turbo Booster for better audio quality, or something like that.