Robben admitted he wanted Van der Vaart to join him at Bayern, and is sure Tottenham have made a shrewd move.
He told the Daily Star Sunday: "I don't know why he didn't join Bayern in the end. I really wanted him but Spurs have bought a gem.
"He is that bridge for Spurs that makes them go from a very good Premier League club to a team capable of taking on and beating any side in Europe on their day.
"Madrid almost gave away one of the best players in the world - but that's their style.
"They got rid of me and Wesley Sneijder in the same summer and I went on to win my domestic league and get to the Champions League Final while Wesley went on to win the Treble and become the best player in the world.
"Madrid's mistake will very much be Spurs' gain."