I thought it definitely helped. There are a couple of reasons why:
1) "Overtraining", so to speak, made the standard-length MCAT much more manageable. The R versions of the tests are 100/85/100 min vs. 70/60/70 min, so one can get through the extended tests, it prepares one well for the mental fatigue you see on the real thing.
2) Extra AAMC material is always better! The MCAT passages have a particular style, and adapting to how the test asks questions is a good thing. Also, seeing more material gives you more opportunities to flesh out weak points and improve them. It only takes one blown passage to take seriously drop your section score.
On the other hand, I took these tests as PDFs on my computer (and wrote my answers on a sheet), and one should make sure to take at least a few of your MCATs (10 and 11, ideally) from e-mcat.com as CBTs, to get used to the format.