With computing power more than sufficient, screen size and resolution optimized, battery life is decent and the devices are fairly durable, the smartphone frenzy appears to be hitting a wall. The only place I see where big improvements can be made to entice people to upgrade is improving their cameras and letting the device become multi-functional (i.e laptop, desktop, tablet processing cores) through use of docking stations. Heck, the connection could probably be done wirelessly.
I would spring for a smartphone with a good optical zoom, RAW file output and some good in-camera processing options. Asus has a ZenPhone Zoom that has gotten my interest.