You're probably right - Ideally, I think very few props are worth that 500k+ mark.
Klemmer is just metre eater, solid first up contact, and great leg drive to generate post contact metres. I personally think Napa falls short in all these categories when you stack him up against Klemmer.
That being said, I would rather have Napa right now, given how the ordeal shaped last season. DK wants to play finals footy - good luck to him. Funny - 23 rounds in, and were in the exact same position, despite a star-studded roster.