I agree with a lot of your points however I think pitching is our biggest priority now and Shields serves so many areas in relation to our rotation and the pen in a trickle down effect, he's the biggest need bar none for us at the moment. I also disagree with Shields being a roadblock with a 4yr contract as the young guys are all under team control for some time and we can get creative with their extensions if need be via more backloading, etc.
I do agree with your stud & dud philosophy specifically, theoretically that's exactly how you should run a team a la the Oakland A's but with a slightly higher payroll to retain more players but we're in a different situation and I do think it is a win now situation for us. Like you said we can't hinge it all on Bautista because anything can happen but the window (physically & contractually) is the next few yrs for the majority of our core- Bautista, Encarnacion, Reyes, Martin. These guys are special players and their time is now.
Personally I think AA should take a serious run at Shields, his signing alone clears up multiple holes on the pitching side and if not then definitely go clear up the other holes (2B, etc.)