You're absolutely right: KDE is, sadly, a developer playground. This is exemplified by the frequent regressions, rewrites of core functionality instead of fixing bugs, and lack of attention given to basic stuff like the Network Manager Plasma applet (how can a DE claim to be serious when it lacks a polished, simple network UI?). I still use it, because KWin is great, and I can configure Plasma to be nearly like Kicker was, and Dolphin is pretty good.
But if there is anything the KDE project is short of, it's vision. There may be individuals, like Seigo, who have a vision for their personal ideas and code, but that is not the same as the project having a vision. There is no leadership of the project as a whole. Each developer does what he wants with his own code, including dumping it and leaving it unmaintained when he feels like it, or releasing a complete rewrite that lacks existing functionality. There is no vision for the desktop UI as a whole--it's just a hodgepodge of Plasma applets.
If this trend continues, KDE will fade into obscurity. I don't like the way GNOME has developed GNOME 3, cutting off their face in spite of their nose (think about it), but I will say this: they have a vision and they are executing it. KDE would improve tremendously if the devs would submit, to some extent, to a leadership with vision, and spend a bit more time on the less-fun aspects of coding.