The "New" 3DS is a stop-gap system to bridge to a new system in 2016 or 17. This new system may be a powerful handheld, a tablet, a fusion console or something else and may be expensive. But 3DS interest is lagging, and New 3DS will likely boost it for a year or two.
But more importantly, what is clearly happening is software development is moving to Wii U, and possibly to new handhelds and/or consoles. Nintendo can't support 3DS fully and prepare the successor(s). Solution? Give a slight power upgrade and new controls, and then port Wii software. 2015-16 could see a half dozen Wii Ports like Xenoblade, Mario Galaxy, Zelda:TP and others. This should stimulate sales to late adopters who are also anxious to try the large existing 3DS library, and hardcore fans will trade in and upgrade.
But most importantly softare resources can focus on the coming next-gen and prevent a softare drought that recent Nintendo launches have seen. Iwata has already aluded to this unified future where titles can be shifted from home console to handheld and vice versa to prevent software gaps. We all expected it, but probably not in this format and not this soon. I think it's very smart.