There is little doubt that money is an important factor in a person's job satisfaction. However, after their basic needs, such as housing and food, are met, a person's job satisfaction is far less correlated with their income than one would think. In fact, most studies have shown that intrinsic motives (such as curiosity, enjoyment, accomplishment) play a larger role in job satisfaction than so-called extrinsic motives. I disagree that money is a primary motivator for employees because not everyone values money equally.
In general, workers' performances are not affected negatively when they are paid more money. According to Chamorro-Premuzic (2013), there is no consensus that the overjustification effect demotivates people, i.e. that extrinsic motives outweigh intrinsic motives when workers are paid more money (Chamorro-Premuzic, 2013, internet). In fact, a meta-analysis of 128 studies found that negative effects were consistently associated with increased monetary rewards (Chamorro-Premuzic, 2013, internet). After a certain plateau was reached (in this case, $75,000), increased income had no effect on job satisfaction (Chamorro-Premuzic, 2013, internet). Thus, while income is associated with increased job satisfaction, this is only true to a certain point, after which diminishing returns are observed.
Not everyone readily dismisses money as a primary motivator for work performance. Granted, other studies have yielded evidence that money is not only an extrinsic motive, but that more monetary rewards translate to increased performance quantity -- whether work was completed by test subjects in the laboratory or actual employees in the workplace (Gupta & Shaw, 1998, internet). Moreover, many studies from this particular meta-analysis show that there is no negative correlation between money and intrinsic motives (Gupta & Shaw, 1998, internet). Thus, these studies conclude that, regardless of the work being done, more money means higher quality of work performed.
However, problems abound with studies that show money increases work performance across-the-board. These studies do not account for individual personality differences with respect to employee engagement. That is, some people may prefer more money, but other people may prefer rewards such as job satisfaction over money. For example, according to Chamorro-Premuzic (2013), a meta-analytic study of 25,000 subjects found that personality differences accounted for 40% of the variation in job satisfaction (Chamorro-Premuzic, 2013, internet). Thus, money is but one of many factors that are correlated with job satisfaction, and it is not even the most significant factor.
The old maxim, "money makes the world go around", may be true for a lot of people, but it is not a universal truth. Science is overwhelmingly confirming that there are "different strokes for different folks". Monetary rewards are only important to a certain point, and personality is a more potent predictor of job satisfaction than any other variable. Although money is certainly one factor in job satisfaction, I adamantly disagree that more money equates with increased job satisfaction.
Chamorro-Premuzic, T. (2013). Does money really affect motivation? A review of the research. Harvard Business Review.
Gupta, N. & Shaw, J.D. Financial incentives are effective. Compensation & Benefits Review 1998: 30 26