Okay, I finished this article: http://fallout.wikia.com/wiki/Fallout:_New_Vegas_add-ons

I'll let you draw your own conclusions, but I think Honest Hearts is going to be a lot better than Dead Money. If only because of having the Burning Man and New Canaan in it.

So I pose a question to all of you New Vegas gamers. Will this DLC greatly enhance the Mojave's plotline or will it just be a short time-waster?

(Note: All DLCs other than Dead Money are TBA with not much info.)

I think they will be a largely separate plotline, with little to no change to the Mojave.

I agree. That seems to be the general trend.
I like both the self-enclosed short stories like the Pitt and Dead Money, so I'm not too bothered. I'd enjoy seeing a DLC that adds extra content to the base map, though, or even added areas to the blank spots on the map we have. I climbed up past the invisible wall down in the SW and wandered around that empty area and there's lots of room there. (I didn't see it, but supposedly there's a door to the Sierra Madre over the hills west of Goodsprings. It'd be sort of cool to see it out there for real.)