I personaly dont see any thing wrong with adding solo instances. Whether you group, raid, or just want to solo all the time , there is days you just want to go off by your self and be away from everyone else. And there is nothing wrong with that.
Also I dont see a problem with solo instance giveing some decent treasured gear. The gear should reflect the difficulty of the task at hand. An easy zone should give low lvl loot , medium range in diff. should yeld decent loot , hard diffculty should yeld some good treaured gear.
The one problem with dungeons and thier solo areas is often they are over ran by to many players and then the plat farmers/sellers take the area over eventualy. So yes imo I would like very much to see solo instances put into the game for higher lvl areas and future expansions.