If you count DLCs in, then yes, I'm a bit ashamed to admit I have. I only bought a couple for the Fire Emblem games on 3DS, since they were story-focused maps, but I didn't spend more than 5$ on either.
As for expansions, I always resisted the temptation. I remember hearing about The Sims' expansion packs a lot when I was younger, but the idea of buying them never even crossed my mind (maybe I simply didn't like The Sims enough).
One of the expansions I loved the most, though, was Shovel Knight's. They released all expansions for free to everyone who already owned the game, and so I ended up with three great new modes. I freaking love Yacht Club.