It was pretty good, possibly even one of the best Rarity episodes. All the details and references in the episode were top-notch and we even got to see Sassy again - not that she had a big role, but whatever. I haven't watched many black-and-white movies in my life, but I enjoyed the noir scenes a lot. They really added something to the episode.
The Wonderbolts' comeback was somewhat disappointing - not that I didn't want to see them again, but because they once again acted like jerks. How could they possibly think Rainbow Dash was behind Spitfire's disappearance? What happened to "innocent until proven guilty"? Not even counting all the times RD has helped save Equestria, you'd think that at least Soarin would have remembered everything she's done for the Wonderbolts themselves. Why does Rainbow Dash look up to these guys again? Oh wait, yes, I know - because she's quite the douchebag herself sometimes. That said, I did like her in this episode. All her character development seems to have finally sunk into her thick skull, because she was being incredibly modest and overall not obnoxious in this episode. Heck, I might even say that she's now too GOOD for the Wonderbolts - that is, as long as I'm allowed to pretend that that horrible abomination of an episode, Tanks for the Memories, was just a bad dream.
Back to Rarity, she was great. We learned that she's a fan of detective novels, how about that. I guess we know now what kind of books she likes to read in her silk pyjamas on Sunday mornings. Screw that cake episode, this is how MLP should do detective stories all the time. Of course, we all knew who the real culprit was, but it was still fun to watch Rarity figure the whole thing out. I swear I don't believe in the "unicorn master race", but maybe they really are the smartest ponies in Equstria. Well, at least when compared to the Wonderbolts.
So, basically, I'd say this episode's pros outweigh the cons. My final score is 8.5/10.