The Vita has a power advantage that could actually position it to a point where any Nintendo successor to the 3DS, means the Vita is still capable of running that software (so "HDS"/Vita dual format releases could potentially end up being much more common place than 3DS/Vita ones are now). The Vita is also starting to attract Japanese developers who I'm guessing are wanting this extra power to be less constrained by hardware limitations which could help drive sales.
I don't see Vita ever catching 3DS, but I do think it could have a much longer lifespan meaning in the long run, it doesn't look like the utter decimation that 2013 sales comparisons showed.
As for Vita peaking, it may well have done in the West unless Sony do something about it. It looks like it's just starting to wake up in Japan though.
RIP Dad 25/11/51 - 13/12/13. You will be missed but never forgotten.
