N. Illinois is one of the worst teams to have made a BCS bowl (though there have been a couple of really crappy major conference winners in there too). For the most part the small conference schools have had too few rather than too many opportunities though.
FWIW, N. Ill. has a 30% chance of winning against FSU according to Ken Massey.
That is higher than the chance he gives Notre Dame of beating Alabama (28%). Interestingly, none of the five BCS games are the tossups you would expect in BCS bowls:
Florida (96%) over L'ville
Alabama (72%) over Notre Dame
FSU (70%) over N. Ill
Stanford (70%) over Wisconsin
Oregon (69%) over KSU