Don't think the Vikings needed to/were going to make any big signings with or without Cousins. They're interested in Bryce Callahan, so you may see a lower tier signing like that or two. Could also see them bring in a vet backup like a Matt Moore, unless they really trust Sloter. Plus they have to save as much money as possible to pay Barr, Kendricks, Diggs and Hunter.
I'm not a fan of shelling out big money in FA anyway. They seem to bust more than they work out. For every Linval Joseph or Captain Munnerlyn, there's a lot more Bernard Berrian, Madieu Williams, Remi Ayodele, John Carlson, Greg Jennings, Alex Boone's, etc. Build through the draft, supplement through FA (guys like Keenum, Newman, etc).
Before Joseph you have to go way back to Antoine Winfield, Pat Williams and Steve Hutchinson in 04, 05 and 06 for good signings, which predate Spielman.