I just picked up DoN about 2 weeks ago, and am still getting into it, but I'd have to say it's worth it from what I've seen.
The guild lobby is great. The new cultural armor is better than my VT gear, although if you're going to make it yourself you're in for a lot of tradeskill time. And the DoN adventures give you crystals to use to buy gear and augments. Which are suprisingly good, and not near as expensive as the LDoN adventure gear was. Plus, the crystals are tradeable so you can purchase from other players if you're short for that next upgrade.
I haven't gotten DoD yet, so can't really help ya there.
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Some people are like slinkies, they aren't really good for anything, but they still bring a smile to your face when you push them down the stairs.