I have the same proplem on my Rev 3. No front brake! I removed the pads last night and they are worn so that won't help matters. My pal who is a bike mechanic is coming round tonight to have a look. I did notice when I was removing the caliper that there was a lot of brake fluid on the disc and pads, upon closer inspection it looks as though the bleed nipple was leaking, I have now tightened this and I hope this was the cause of spongey pressure and naff brakes.
I keep reading about how difficult it is to bleed Beta brakes, I have ridden bikes for years and the brake system looks just like any other, so why would it be such a pain to bleed? I guess I'll find out tonight!
I agree with Graham, swapping to a 2 pot will not be the answer and will only add to your woe's.
Ash