Putting a minimum spending floor is the only way to force tanking teams to hire players with skill.
Are you trying to say, there are no overpaid players in the NBA? LOL. You can just check how many teams have used their amnesty exception. You can look at the salaries paid in 2011. Although you have to be familiar with the NBA in order to know who is overpaid. Reading NBA.com once a week is not enough... I can throw in a few names: R.Lewis (22.1mil), G.Arenas (19.2mil), A.Jamison (15.0mil), B.Davis (13.9mil). Although I would never have signed J.Johnson, E.Brand, R.Gay to max deals and are currently overpaid, they still do produce at a decent level.
I had a suggestion about how salary floor could be calculated, some time ago. Belgium has 440 users, so basically divIII is their lowest league (leaving only 104 teams to divIV - enough to fill 6,5 leagues out of 64 divIV leagues). Ofcourse you can win lower divisions with all SF lineup. Every competition level needs to be looked at. The salary floor might be fine in the lowest league. It's not fine currently in the top divisions.
Your goal should be winning, not spending more money than the next team.
Nobody is forcing you to spend anything. But you will pay the minimum salary floor that is considered "competitive" in that division level.