Are you 100% certain Williams is going to fall to Miami at 12?
You can make a 100% certainly in the pursuit of someone via trade. You can target Williams all you want...but there are 11 teams in front of Miami that could either take him or trade out so someone else can get him.
That is what I'm scared of. It is entirely possible that Buffalo or Denver could snatch up Dan Williams. I, personally, wouldn't see that as the end of the world because we would just take Jason Pierre-Paul, and he is going to be the next dominant rush LB in the league (6-5, 270 lbs, and runs a 4.64 forty)...either that or another Vernon Gholston (highly doubtful though).
This is widely considered the deepest draft ever, and next year (if there is a next year) is widely considered the deepest free agency class ever, so I say use every pick you can this year, and if a WR doesn't emerge from all of that, pick up one next year.