To respond to the title of the OP, rather than rehashing the abuse of an expired equine, I have one interesting and creative use for Detect Magic: Find The Swag.

Character was a Rogue/Nightsong Infiltrator. Took the PrC because it was fun, and supported the party well. So I got Detect Magic at will at 4th level. So what did I do with it? I used it on every NPC I walked by, to see if they had anything worth stealing. Sure, I ended up with a few handfuls of Nystul's-augmented fake stuff, but I also scored some pretty sweet swag with a few Slight of Hand rolls.