Not sure I agree about the Packers, as the Pack gets very few high level free agents. Reggie White came for two reasons, a ton of money (pre salary cap) and Brett Favre. Woodson came because his value on the market wasn't what he thought it was, and the Pack overpaid (at the time, looks like a steal now). Can't really think of another high level - highly sought after free agent that came to the Pack.
The Bucks are not going to get top level free agents, so they have to somehow find a core of players through the draft, and then sign mid level guys that can play around them. Not easy to do as the NBA draft is about as much of a crap shoot as anything.
Right now the Bucks have to decide if you can build a winning team around Jennings and Ellis. If the long term answer is no, then trade them and move on.