You two are really dense. Do I really need to say again that I am not endorsing running with a weighted vest? Are you so bent on being right that you have to put words in my mouth? Repeat that for weighted bat, kettle bell and ankle weights.
Regarding mechanics of running. A weighted vest would not increase an athletes foreward lean. The added weight would increase his tendancy to stay upright. So, if your concern is foreward lean, your concern is unfounded. Again, do not take this statement as an endorsement for running with a weighted vest!
Have you guys heard of cross training? I know, I know, cross training is an old concept. It's out dated. It's not on the cutting edge of training like you guys are. Well, anyway, cross training does not screw up mechanics it increases adaptability.
Speaking of adapability and weighted bats. Most major leagers swing a weighted bat. When I played, in the off season my wife would pitch me wiffle balls which many would argue is a bad idea. After all wiffle balls slow down much more quickly than baseballs and this can lead to a late swing when switching back to a hardball. However, making these types of switches improves a hitters ability to adjust. You don't always get a fastball down the middle. Sometimes what you thought was a fastball down the middle turns out to be a slider at the laces or a change up. You have to be able to adjust your swing.
When I hit wiffle balls I often used a weighted bat. Partly to increase strength, partly to increase my ability to adjust and mostly so I wouldn't kill my wife. A wiffle ball crunches when you hit it and moves very quickly before it has a chance to re-expand. I would still always take some cuts with a regular bat at the end and I can tell you with certainty it didn't screw up my swing.
Although I don't endorse running with a weighted vest I do endorse Plyometrics with a weighted belt. a weighted belt stays snug against your body and is reasonably comfortable. You can get a nylon belt with pockets and little sand bags to go in the pockets from a dive shop. I use to use the weighted belt at advanced stages in my plyo programs.
It sounds like you guys are fans of Dr. Chu's Complex Training. His books are written to about the 8th grade level to appeal to a broader range of readers. Doing a plyometric set with a weighted belt, then doing a set without should appeal to you. This is assuming you are intelligent enough and flexible enough to believe that the Complex training does not have to consist of a fast movement following a near maximal load.
I guess I've said enough.