As a player I don't really give a shit about sales. I only care about accessibility. So the fact that VC ports for the 3DS "aren't necessary to boost sales" is of no relevance for me. Besides, to Nintendo it shouldn't matter if they "need" the sales, only that they can get the sales. Sales are sales and throwing a bunch of VC ports at us equals more money for them for minimum effort. It's win-win.
Furthermore, "we don't need VC titles for both consoles" seems like an incredibly snooty thing to say. Like, I'm sorry that not everyone has infinite money at their disposal, but chances are a large chunk of Nintendo's customers don't have the funds to buy both a Wii U and a 3DS, so they'll have to pick one over the other. I happened to pick the 3DS, and you're basically telling me I should get the shaft because lol, making classic games accessible for both options isn't necessary. Those guys who bought the less pricey console can suck it.
I'd love to play games like, say, Super Metroid on a modern console, without having to purchase decade old cartridges from ebay, and the 3DS is perfectly capable of running those games. There is no reason to declare this infeasible, especially not "it's not necessary".