It's not necessarily how hotly contested a ruling is likely to be that drives whether SCOTUS will take a case. Sometimes it is, but if you take a tally of the votes from SCOTUS rulings, there are few 5-4s, and lots of 9-0s and 7-2s.
Which cases SCOTUS takes is driven largely by what issues they choose to address and the points of law they are trying to make. Collins presented important issues involving the exercise of governmental power: particularly separation of powers, accountability of the executive branch and the limits of its authority where private property is concerned. That's why I think they took it, and judging from the tenor of the oral arguments, it would be a mistake to simply count liberal and conservative heads.