I have to admit, even though I started buying my boxes before Well of Darkness released(I have all, up to Road to Legend), I have a bit of a sour taste in my mouth after spending over three hundred bucks on a game system, only to have them change to a new edition. I love this game, and this company, but this is kind of disappointing to me.
It never ceases to amaze me that some people are surprised to learn that things change. Any commercially successful product will eventually reach a point where it needs to be redefined, to cut the bonds of the past in order to continue growing int he future. Movies get remade, cars get new models, board games get new editions. If this doesn't happen, the product stagnates and falls behind, gets forgotten in time.
Descent first edition is a perfect example of this; I loved it as much as anybody here, but I would be remiss if I didn't admit it was getting bloated with all sorts of rules that didn't really work that well together. Expansions were reknown for introducing mechanics that never saw the light of day outside the quests that came with it. Half the time, FFG's answers to rules questions only served to raise even more questions. The fact that the fans felt the need to begin that huge FAQ project at all is proof enough that things were getting out of hand (I still have my fingers crossed that they get their answers, btw. They deserve it after all the work that went in.)
However, just because second edition is coming doesn't mean you've wasted your money buying first edition products. For one thing, there is the conversion kit, as you've mentioned. I'm quite sure that fans will make homebrew rules for any terrain or other props that don't appear in the 2e base box in relatively short order, too. If you're not inclined to do so yourself, just wait a few months after release and see what's around. You don't need to buy 2e on release day if you're not sure about it. Wait a few months, try to find an FLGS you can play it at first. Make an informed decision.
And, of course, no one is putting a gun to your head and stopping you from playing first edition. You don't have to burn all your old boxes just because there's a new kid in town. You can safely ignore 2e and save your money, or if you really want new 1e material, you could consider picking up 2e and making homebrew rules to convert it backwards. I'm sure you wouldn't be the only one interested in that, if you're so inclined. Or you could just focus on making fan quests using what 1e has already provided you.
Of all the gaming companies I've known, FFG is the most conservative about releasing new editions. That's not to say it never happens, of course, but they're generally pretty good about recognizing what games need an overhaul and what games are well enough as is. All bickering about the particulars aside, the fact is that Descent needed a new edition. To keep going in first edition would only have made the game system more bloated and less logical than it already was. Maybe you don't like how 2e is shaping up, and that's your prerogative, but this is something that needed to be done sooner or later (and I seem to recall having said so several times, long before FFG announced 2e.)
Descent has been kicking around for 7 years now, and the average lifespan of editions for most board games/RPGs is roughly 10 years, in my experience. That is to say, after 10 years, a game will either have seen a new edition or it will have gone OOP. Which would you prefer for Descent?