I don't think this is invalid, but at the same time, it seems like it's suggesting that, rather than searching for a need you want solved and framing it in terms of a realistic goal and whittling it down to a compelling product, you should be identifying someone else's need and building that product.
A fun idea without a plan may need some serious thought and modifications to make it a compelling product, but I think that perhaps a compelling idea with no fun is pretty difficult to make fun.
Perhaps my core philosophical objection can be summarized in contrast to this:
> Any sufficiently big market will give you tons of interesting ideas. Why do you need to come up one of your own?
I don't think this is a market-driven approach, in the sense that the market is merely setting the context, and it's still interest-driven, and you're still searching (and hopefully coming up with) ideas you find interesting. Just identifying exploitable needs isn't necessarily going to expose something you're going to enjoy.