While I like sometime a good solo instance/dungeons, I wasn't really in favor of one rewarding raid loot. Then again, I remember that we're in a situation where raid loot is giving away by world boss, so he, why not. If the instance is difficult enough and limited at once a week, it's fine, it's no more easier than farming the WB once a month.
I like some idea posted here. Randomized element, having to be quick and efficient otherwise boss is buffed more, and so on. Some mechanics are already thgere in the Idea in the existing Solo dungeon - Dead Man Hand have a randomized boss at the hand, each one being very different (DPS Race, one where you're -hum- "supposed" to interact with lever, and so on); there's some platform puzzle in the Refuge, some interesting mechanics in Forgotten City... Some solo instance are actually really nice. And some should be mandatory for low level because they teach you basic tropes. Pyramids of the Ancient, for instance is great, and learn you to pay attention to buffs/debuffs, to interrupt cast and so on. It's not as good as a 6man or a raid to teach you how to play in group, but that's already something. And I believe Funcom can push the concept further with harder and more demanding solo dungeons that keep you on your toes.
That's true, it has been a long time since solo players got some new content, even if the partly solo arena is on the corner.