Yeah, as much as its fun to laugh at The Letter, the fact that people started to buy it as a joke and it ended up selling well...
If this becomes a trend, it really wont be good for the eshop
Yep, people gave it so much attention, that even if it was all bad press/etc, it made the game sell better. It certainly makes devs second guess the eShop if people won't bother with other games. The Letter may make people laugh, but if that is the only game off the eShop that gets attention (besides big indies that would have gotten attention anyways) rather the other games, like mine, that has barely a presence outside certain areas, it doesn't bold well for eShop.
People mention advertise, but advertise how? A banner ad doesn't really do as well if it can't link directly to a download site (since no web-eShop yet). Articles & interviews can help a lot of course. There is also likely issue that some of us aren't that knowledgeable about how to advertise our game to make it more well known. I had that issue for sure. Luckily I'm teaming up with someone who mastered in marketing for my big 2015 title.