Certificate in data mining
As with any certificate course, it really depends on what you intend on getting out of the program. All of those are well-respected universities, and the coursework will almost certainly be extremely informative. In that regard, you'll learn a lot. On the other hand, there exists a frankly ridiculous amount of high-quality, freely available information online related to data mining from many universities, including some of those you listed above, so you can definitely learn all that without paying a not-insignificant sum for the experience.

Regarding job prospects, it really depends on where you're looking to be hired. This answer from Workplace.SE is an excellent overview of how useful a certificate can be in helping you get hired, and this question from Programmers.SE has many useful answers discussing how certificates like the ones you mention are viewed in industry. Long story short, they're usually not that useful for jobs unless they're industry standards, which the ones you list are not.