While Nd4 certainly gives White an advantage, it certainly doesn't make the move Qa5 "really bad". 

Either way, with new systems, lines and novelties following 1...d5 and KID coming under scrutiny (not to mention the plethora of theory involved in playing both moves), we may see new life pumped into the Leningrad Dutch. Susan Polgar has an entire article on the 7...Qe8 line in the August 2003 Chess Life and she seems to feel that the Leningrad Dutch in an agressive system against 1. d4 and is a good alternative to the KID.

Although NCO seems to be of the opinion that 7...Qe8 is best, I've uncovered an interesting sideline which runs 7...c6 8. d5 (nothing new) 8...Qa5!? which David Bronstein used to beat Colin McNab at a tournament in London in 1989. Given that Bronstein felt that it was good enough to use as an alternative to his signature King's Indian Defense, I think it is certainly a good try. The only testing reply is 9. Bd2 which, at the very worst, may be slightly better for White. Then again, that's what they say about most of the Leningrad Dutch main lines.