Same here. (R.I.P. Club Penguin)
I did manage to accidentally spend $350 on HearthStone a couple of years ago; and, while the game did provide a few fabulous all-nighters (during one of which I made it all the way down to “level 6” with my Dragon Warrior deck), it might have been a “slight” waste of time and money (and my wife was not particularly appreciative of my accomplishment).
On a related note, seeing as how time is money, I used to bake cupcakes in the YoVille factory (for credits to buy dresses for my wife’s character -- there was a blue little number that ended up looking fantastic on her). This was especially ironic since irl I was often between patients (i.e. at work) when I would hit the factory floor. Eventually, I figured out how to wear leopard-print speedo’s "in public" on YoVille, and that ultimately made the entire experience worthwhile.
I've only spent money on a mbile game twice, and that was to get rid of the godawful banner adverts. And even then it was about 99p on an otherwise free game.
DLC wise, though...
Fallout 3 + New Vegas, have all the DLC for both. I got the season pass for Vegas, although 3 was brilliant because I got the discs with two of the dlc on through a DVD & Game rental service I was subscribed to, so technically those didn't cost me anything I wasn't already spending.
Elder Scrolls: Oblivion and Skyrim: All the DLC for both again. This time it was a bit more piecemeal, though.
Borderlands 1 & 2 - All the DLC for 2, as well as the Gaige character pack, skipped out on the other one though. for 1, I think I only picked up a couple of them, but I didn't play that one online, so it wasn't really as important.
As for regretting DLC purchases, probably all of the update packs for CoD Black ops 2 - There was a patch that went out one summer that just completely killed the game for me, as I used to play hardcore S&D almost exclusively with a close team of friends, and it just made the "sprint and spray" classes that where already a blight on the game way too OP to the point that was all anyone was playing.
One of my mates has probably spent a good couple hundred quid on his Star Trek Online account, as well as having paid about £300 for the lifetime subscription before it went .Free2Play.
Growing up, there weren't a whole lot of pay to play games, so the thought of spending cash to play has always made me doubt certain games. At most I've spent ten bucks here and there for dlcs though, if I thought they were worth it. I've always had more fun in games earning stuff, or murdering the owner for it instead of using real money for shit.
Crusader Kings is my black hole >.>
The most i've spent is probably 60 dollars pre-ordering star wars battlefront II
Probably like $20 on CS:GO skins
I think as a kid I've spent, collectively, over a period of multiple years, maybe 120 bucks on MMOs. But then I realized, "Oh, $120 is a lot of money! I had to mow lawns for entire days of my life for that! I should remain a free to play scrub."
I then realized that half the ones I was playing were pretty shit unless you were part of the bourgeoisie elite, and quit most of them. Then I started quitting the o es that were more entertaining on their own merits the more I learned to hate children.
Now I only drop money on TF2 cosmetics. I know, terrible financial decision on my part when I could just wait 10 years until they're all free once people have quit the game entirely and the program is no longer supported by Valve, but I make do.