The Washington Post's headline is "Spending by independent groups had little election impact," and documents how groups like American Crossroads spent hundreds of millions of dollars to little effect. Traditionally progressive-aligned groups like the SEIU's elections arm, on the other hand, had great success in backing candidates who won. Big Government's Mike Flynn has a piece along these lines:
Enormous financial resources were wasted by the GOP's consultant class. The GOP brand itself has been badly tarnished. Over the coming weeks, we will shine a spotlight on this consultant class. We will even name names. Its long past time the GOP rids itself of its own internal corruption.
There might be a different effect at work here: when it comes to just money, amounts don't particularly matter. University of Chicago economist Steven Levitt has studied campaign expenditures and found that they have very little effect on the business of winning elections:
What Levitt’s study suggests is that money doesn’t necessarily cause a candidate to win — but, rather, that the kind of candidate who’s attractive to voters also ends up attracting a lot of money. So winning an election and raising money do go together, just as rain and umbrellas go together. But umbrellas don’t cause the rain. And it doesn’t seem as if money really causes electoral victories either, at least not nearly to the extent that the conventional wisdom says.
It could be the case that many of these candidates and campaigns were poorly run - GOTV failures, for example - but it has little to do with the money. It's difficult to say that wealthy donors were ripped off because their money wasn't spent wisely. It's more likely that wealthy donors were ripped off because money isn't what wins elections.