The Dolphins are not the first team to have $100+ mil. in cap space to spend on free agents. Every year there are a handful of teams, awful teams, with money and a delusion they'll work the f/a market to fill the many holes their inept team management and scouting have left on their rosters and every year they just manage to overspend on replacement level players that don't make the team better, at all. The Raiders and Jets did it this year, the Browns the year before, the Jags the year before.
When teams like the Dolphins shop the market they will grossly overpay for subpar production because it's the only way any free agent is coming here. A bunch of good teams: Colts, Cowboys, Ravens, Seahawks, Bills are going to have $80 mil.+ to spend in ufa next year, if you're a quality player on the market you're going to one of those teams unless a bad team grossly overpays like the Raiders did for Trent Brown and Tyrell Williams, like the Jets did for Trumaine Johnson or Kelvin Beachum, or the Broncos did for Ju'wain James. The Texans paid a career backup from the Jags, Aaron Colvin $34 mil/18 guarenteed, to play CB only to cut him one year later.
These are the exact kind of guys the Dolphins will bring in, they're the only kind of guys that would come. I remember a few years ago when the Giants paid Olivier Vernon $70 mil. to suck, everyone was astounded a team would pay a guy like that that kind of money, well prepare to be astonished by what this organization will pay for comparable talents next year.