Well, he has been "worth it", essentially his entire career.
Shields indeed has been very good. He's just not been great. I wouldn't say that he'd be a bad deal, if he pitches from ages 33-36 like he has all along, then he's easily worth $20M a year.
I just would prefer paying for an absolute upper echelon, top 5 or 10 type guy like Scherzer is, even if he costs 33-50% more per year and a longer commitment.
You won't hear one critical word out of me if the O's do sign Shields, that'd be fantastic. I just think Scherzer, even at more money, would be even better. I think both are so far beyond the realm of possibility that they are equally likely to be signed. Signing Shields because we can't afford Scherzer is the same as me saying that sure, I'd take a BJ from Scarlett Johansson but only because Mila Kunis and Kate Upton were too busy to make it to our scheduled threesome.