Sox fans love to say other teams' FA signings are for way too much money. Other big market teams find a way to spend this money without it seriously hamstringing them down the road. The Cubs might be a big exception to that - and maybe the Mets too.
Is $16M for Sanchez too much money? Who knows - teams are raking in more and more money and they're spending more and more money on players too. If the Sox want to be one of the big boys in the AL, they're going to have to keep up with the market. New York, Boston, Detroit, Texas, LAA - they're not shying away from big contracts and they're consistent playoff contenders.
If the Sox answer to this is to point to the $56M they threw at a 1-dimensional all or nothing slugger and say they don't want to get burned again, then they can just sit back and watch other teams pass them by and scratch their heads as to why fans won't support their team.
The other alternative to paying this kind of money on free agents is to develop enough talent from within to fill roster holes.....and we know the Sox have been woefully inadequate in that category for the last decade.