In 2013, the team had neither the money no the inclination to pay Sanders the $16M over 3 years (with $10M guaranteed) that we paid Amendola. Sanders was unproven, and the decision not to pay him move than $5M a year was a relatively easy one. I suppose that we could have made him richer by making the one year offer a bit more; PITT would still have matched.
The real question was in 2014. I believe Sanders. I think that might have signed with us to over $5M a year, with $10M guaranteed. Most of us were surprised to see him get $5M a year from Denver, with $6M guaranteed. In any case, IMHO, the team made a reasonable choice in signing LaFell to a 3 year contract at $3M a year, with $3M guaranteed.
Looking back, I suppose if Belichick knew that Dobson, Thompkins and Boyce would amount to almost nothing, and Amendola would underperform, I guess that Belichick might have paid the bucks. But that is 100% hindsight. Belichick obviously expected more from the FOUR 2014 receivers added in 2013.