Best. Casting.
Period.
Seriously, he has been cast as Scrimgeour. Aberforth and Luna's father have both been cast, and David Yates (who has worked with Nighy) stated in an interview that Bill would be his first choice for Scrimgeour. Bill Nighy is a wonderful character actor, IMO. He may not look physically imposing, but he researches his parts well.
Concerning his "goodie" comment: He probably meant "goodie" in the sense that he liked the role. He wasn't necessarily commenting on the content of his character. Bill confessed that he hasn't read the books yet (although he intends to to gain some perspective on his character's traits), so that could explain why he said the character struck him as "good"...at the moment.
Here are some more images of Bill Nighy: