It's been over 20 years and in that length of time people strongly adhere to their own personal experiences in forming their opinions on this kind of stuff. I fully include myself in that statement.
In my time at Funcoland literally thousands and thousands of NES, Genesis, SNES, Gameboy, Game Gear, carts passed through my hands and as a part of my basic responsibilities I had to evaluate almost every single one before buying and/or selling.
Something caused all the mold, mildew, corrosion, wear and damage to the cartridge contacts of games that had them. Wherever we found evidence of that, I and all of my employees got into the habit of asking the owners of the games "do you blow in these?". Games that had that kind of stuff going on would get a "yes" 100% of the time, so ... there's something here, there's some sound logic and basic evidence.
Anybody who is still filled with a burning desire for MOAR DATA should run with what has already been done and give us some more empirical data to work with.
I'm not doing this again because I swear I almost gave myself a full-blown respiratory infection doing it.
Really though, I just wanted to do something that showed some level of evidence that the act of blowing onto the contacts of NES carts had some kind of potential long-term effect.
Nice to see your cartridge licking made the article! See, it pays to bump old threads!