Not sure if they ever signed an elite free agent. Off the top of my head I would guess that Golden Tate was their highest profile free agent signing.
You do have to be a Super Bowl contender or consistent winner to be considered by elite players
They re-signed Calvin. He didn't have to stay but chose to following 2011 season and huge money. Then got hurt a bunch so quit after 7-9 season and playoff season when he retired.
We have got plenty of free agents that were higher tier free agents at the time like Tate, Bush, Glover Quin, Trey Flowers, trading for Ngata (elite player to replace Suh but old), re-signed Slay, before Patricia pissed him off, you could say re-signed Decker/Ragnow would be top tier free agents too. The current roster has tons on rookie deals (will Sewell (3 years left) , St Brown 2 years left, Hutchinson (4 years left) all stay is the question) and lesser with (Alim McNeil 2 years left , Jonah Jackson 1 year , CGJ re-sign 1 year). This year will determine that as the Lions do have the cap room for them.
And many times they get traded or are older at that point:
Tyreek Hill and OBJ traded (not elite either, just overrated) ,Stefon Diggs traded. But can't force trades to the Lions (players want and compensation package)
Ramsey traded a few times
Von Miller was traded to Rams. But did sign with Bills as older player (and didn't pan out due to ACL)
Khalil Mack traded to Bears and to Chargers
Randy Moss traded a few times and chose to be awesome for certain teams/years
Julius Peppers I believe was a big Bears signing and cut and then a Packers signing
Charles Woodson was cut by the Raiders and signed cheaper with Packers somehow
Reggie White the first big elite player
Brees wasn't elite but was good when signed with Saints in 2006 (but we went with Kitna lol Millen). Culpepper was just as highly rated and was a dud for Miami.
Peyton and Brady, Lions were happy with Stafford and they wanted a win now team
Lamar (not elite) ended up re-signing. Same with every elite QB it seems (Allen, Maholmes, Rodgers (then just now traded) etc)