I agree, but the total light path was only about 10"/25cm.
Yes, that's true but more output means a larger light or a custom battery with shorter burn times. In the FIX case it's the latter. Yes, dimming helps fix the burn times but you still have a custom battery and charger instead of AAs. There's always a cost to more power and it's the cost that's the downside. I always considered the FIX halogen light the best once you were underwater. It was out of the water where I liked it less than the older LED version. 
I see your points and I would also be happy to get a FIX 1000 LED for the same price as the HG20DX. But with standard AA batteries and the same brightness as the HG20DX (for a focus light I'm sure that's enough).
But, that model doesn't exist...
As the 1000LED is said to be twice as bright I guess it's just to like the situation. I really dislike halogen bulbs so getting a HG20DX is out of the question.
What I like mostly about the HG20DX is that its beam is so extremely wide. I would hate to pay more money just to find out that the LED1000 doesn't deliver that extraordinary wide and smooth beam (strong or not).
I doubt I will really have much use of the extra power of the 1000LED, but it could be fun to experiment to use it as a strobe replacement. Not sure if the wide beam is a good or bad thing at that point though...
I haven't seen those images, but the D3 requires an extra 1+ stop of light (over the D300)
Why?
Don't they both have ISO base at 200?
and if you want dark backgrounds you need faster shutter speeds. Yes, you would want even more light as a strobe replacement, but that's not the point! The point is that the focus light, when putting out this much power, will have a noticable effect on your images even when you are using strobes. That's an unintended consequence that people may not be aware of and may not want. White balance for my BigBlue light is not the same as it is for strobes, so if I am doing creative lighting effects the focus light will be washing out my shadows and adding uncorrectable color casts.
True, and something one has to be careful about. Just using full power on such a strong light can be really bad for your shots.
Personally I haven't had the need for stronger focus lights than what I've been using and they haven't showed up on any pictures (except for when I was using a halogen Ikelite Mini C with fisheye diffusor, that ruins my wide angle shots, but when I switched to LED lights I can't even spot them on wide angle shots). My problem has always been that I have to move the focus light constantly. Even thought the spot has been fairly wide (and perfectly smooth), it has never been close to what the HG20DX delivers.
BTW, I wouldn't assume the FIX 1000 is brighter than the BigBlue without testing. It puts out twice the rated light but it may be considerably wider. Also, I'm not stating a preference for one light over the other since I've never seen the new FIX light. I'm simply throwing out some arguments for why another light might be preferred. More power and more beam width are better up to a point, then other factors become more important IMO.
Sure!
But to me a really wide beam, LED, pretty strong and dimable are the most needed features (but far from all wanted ;-)). As far as I know, there are no alternatives...
/Peter