No reason to completely give up on Vitters (or Jackson for that matter) so that is a good point. This signing should open up some opportunity for Vitters since it is virtually certain that Stewart will suck or get hurt before June. Hopefully he gets a better opportunity then his last time up there.
Although it wouldn't surprise me in the slightest if both Vitters and Jackson are wearing different uniforms next year.
It's not that I really love these guys, but I just can't see too many other teams who would value him higher. I think they both just need a team who can give them a full time job in the majors and let them grow (possibly after a month or so to get back on track in AAA if needed). The Cubs don't have anyone significant blocking either of them and apparently aren't going to try to compete next year, so it's a good situation. So I think I would rather the Cubs just roll the dice with them and give them the chance to show some improvement over the course of the year.