Bader is a better hitter than Omar Vizquel, and he got HOF votes! That's obviously not a fair comparison, but Bader is an amazing defender, he really doesn't have to hit that well to be an above average player overall, and really he's not even that bad of a hitter that it really merits discussion.
Carpenter was hurt last year. I really think we'll know by the end of Spring Training if he's healthy or not. If he's healthy, there's no reason to think he won't go right back to being a well above average hitter; his ability to take a walk and spray doubles are hitting skills that usually age gracefully.
I'm like 99% sure, barring major spring training injury, the roster the Cardinals have now is the one they're opening the year with. The payroll being where it's at allows them to be active at the deadline though, which is when the Rockies might be a little more rational about Arenado.