Yes. For the first time in a while I would say Crawford might have been signed for his intangibles.
His tangible assets make him plenty valuable, but probably not at the level of $20m/yr for each of 7 years. However, his intangibles could pretty easily make the contract worth it. Not only does the contract also include the prime years of a potentially Hall of Fame career and consistent playoff appearances, but playing extra games in the playoffs is huge in terms of overall fan interest, merchendise sales, advertizing (both current and future), etc.,.
If his WAR are the ones that take public perception of the team from "maybe" making the playoffs to "probably" making the playoffs, over 7 years that's a lot of value in advertizing and merchandise. Because the team is that close he is a smart investment to get that extra revenue given that he's probably worth at least 17m without the inflation of the current FA climate or any addition to team revenue.
If his next 7 years mirror his last seven, then he would have 2719 H, probably two seasons away from 3000.
He would have 195 triples (8th All-Time).
He would have scored 1497 runs (85th all time), ahead of Rod Carew, Roberto Clemente, Joe DiMaggio, Jim Rice, Brooks Robinson, Tony Gwynn and a number of other HOF players.
He would have 754 SB (6th All Time).
I think you're absolutely right to question whether he's worth that much money in terms of regular season on-field production. In terms of "selling" and the Red Sox as a brand, though, I see him as an investment in the franchise as a whole.