I don't think they've got that many needs. Starting lineup with no re-signings or rookies:
WR: Shakir, Harty
WR: Diggs, Shorter
LT: Dawkins, Van Demark
LG: McGovern, Bates
C: Morse
RG: Torrence, Anderson
RT: Brown
TE: Knox, Davidson
TE: Kincaid
QB: Allen
RB: Cook, Hines, Gilliam
LE: Rousseau
DT: Oliver
NT:
RE: Miller, Jonathan
LB: Bernard, Spector
LB: Milano, Williams
NB: Johnson, Neal
CB: Douglas, Elam
CB: Benford, White
SS: Poyer, Hamlin
FS:
If the Bills re-structure basically everyone with the option to do so on Spotrac, they'll have around $20M in cap space, with around $10M for veterans. The above list has 19 offensive players and 16 defensive players. They'll need 9 defenders and 6 offensive players to fill our the rosters. 10 of them are likely to be rookies, leaving about $10M for 5 players.
They key spots needed are S and DT, with some attention needed at DE and WR. They'll likely use the veteran money to go after those positions.
So I see nothing wrong with investing in the future with offensive line. The Bills OL has been healthy all year and we're seeing the results. Morse and Dawkins will 33 and 31 when time comes to re-sign or replace. I've got no interest in re-signing either at that age. I've got no interest in plugging in rookies. I've got no interest in playing for high dollar players as replacements.