One thing you may want to look for is whether or not a Starbucks moves in. They target areas that are going to be making significant improvement. Northlake, Franklin Park and Schiller Park are three neighboring areas where you would never have thought that a Starbucks would pop up...but they are now there. These are more industrial areas, but as far as being close to a train, Franklin Park and Schiller Park both have train stations.
New expensive town homes and condos in Oak Park just amazes me. But just like La Grange, I think Oak Park is already there.