The big question for dedicated handheld gaming platforms is really a matter of how much of a market there is for $20-50 games in the days where games on Android or iOS rarely ever go over $10, with the vast majority being less than $5.
This isn't even a question of comparing big budget (for a portable games) production values with something that was created by a small team in a fraction of the time, but what the majority of consumers will continue to buy and play on the go. In other words, where the growth lies.
While I think there will always be the children's market to include anyone too young to have their own cell phone, even this market is being erroded in light of all the mini-apps developed for smartphones that are targeted directly at these demographics. I see parents handing iPhones and iPods to small children every time I see a family eating at a sit down restaurant and I know there are volumes of learning apps and play apps that kids love. No need for a DS. Certainly no need for $30 games.
For dedicated gaming handhelds, one of the few remaining reasons for carrying one is to play specific franchises on the go that are platform specific like Pokemon, Monster Hunter, etc. and this particular niche of gamers will remain a niche that simply may not be able to sustain all the projects in development directed at the dedicated core gaming demographic in the near future.
In the case of the NGP, about the only potential general application use I can see offhand without a finished product, is specifically the 3G network connectivity for web browsing and smart phone type data apps (locators, GPS, maps, shopping aids, search apps, etc.). And this would largely be useful only if you weren't already a data network subscriber with a smartphone (redundant otherwise). Since these apps aren't likely to be subsidized by advertisers on SCEs closed development platform, I don't expect to see volumes of these popping up in the PSN Store either as offerings are likely to remain game centric.
I'm still buying one, but I just don't see myself taking it anywhere (same for the 3DS other than to try out StreetPass after which I'm unlikely to ever carry one around again). About the only reason to buy either of these current gen handhelds is specifically for whatever platform specific titles are available now or in the future.
