The only deal I would definitively say was an overpay was for Kimbrel. The Sox gave up two BA top 100 prospects at the time, along with another pitching prospect in the top 10 of a deep farm, and took on the entire contract.
Fans criticize the Thornburg deal because it didn't work out. But to give up a decent 1b/3b and an unranked INF prospect for 3 years of a pre-arbitration closer seems like the cost of doing business. Actually, compared to what other pre-arb closers like Ken Giles went for, it might even be a cheap deal. But it became a bad one because Thornburg got hurt and never recovered and Dubon panned out...