"A player who was better than league average -- several years before -- who is now in the decline stage of his career and now has a low ceiling but also an established floor -- rather than playing a young player or players with much higher ceilings, but also no established floor."

Did you not read the part about Stewart being under a one year contract?  If this doesn't work, he's gone at the end of the year.  

"Stewart would be the kiss of death for this team as it would take more AB's away from players more likely to be productive."

These younger OF players like Murton and Pie are NOT as likely to produce as much as Stewart in the next two weeks.  Murton is batting .256 and Pie is batting .214.  We don't have time for Pie and Murton to find their batting stroke.  Stewart is hitting almost .300 right now and knows what it takes to make it to the MLB playoffs.  

This is not a typical Cubs move because we aren't typically in the hunt.  If we were 10 games under .500, 15 games back from first, then yes play the kids, but this is the final stretch and the kids aren't cutting it.

Don't ignore the Jones effect either.  I think that could be a boost all around.