It's difficult to immediately tell if a team has overpaid since when prospects are involved it may take years to determine their value.
IMO there are two trades that right now are not overpays because of where we'd be without them:
Chris Sale - We gave up Moncada, Kopech, Basabe, and Diaz. I could be wrong but I don't see any one of those being the impact player that Sale is. Maybe two of them will equal one Sale, but at the same time.... you don't pass on Chris Sale.
Craig Kimbrel - We gave up Margot, Guerra, Asuage, Allen. How much is the best closer in baseball worth?
The upside of these multi-player deals is that most likely not more than one of them will be franchise-type players and there's an even chance that no more than two of them will be regular players. Sale and Kimbrel are the players that a team with the record like Boston has had since 2013 has to acquire if they want to win in the near future. The cost may be high but it fills a need.
Wade Miley and Aro for Carson Smith. I guess you'd have to say right now that this was an overpay but since Miley and Aro aren't the type of player to fuel a championship team and Smith could be one of those guys. I'm not unhappy with the trade.
Getting Thornburg for Travis Shaw, Dubron and Pennington is the one that looks the worst right now. It's looking more like Thorn is going to be out all season and Shaw could fill our need at 3B. While the Travis Shaw the Sox traded isn't the same Travis Shaw who's currently playing for the Brewers, at the same time Thornburg is giving us nothing while Shaw now looks like a serviceable 3B-man. It looks like we got the worst of this one.
We got Pomeranz for Espinoza. At this moment I'd have to say that we got the best end of that trade, but IMO this is the one that has the best chance to turn around and bite us too.
I'm not as concerned about "the cliff" as some are because that cliff is 4-5 years down the road. Had I been thinking about the 2017 team back in 2012 or 2013 I wouldn't have surmised that most of our current players would be on the team. Players develop, trades are made. I'll start my hand-wringing in 2020 or 2021 if it looks like we're going to be cellar dwellers again in by 2013.