I'm not completely opposed to the idea, but I don't see it bringing in any new ideology to the governing system. A former politician, although running as an independent, will likely still make decisions based on their former party affiliation.
It would be better to implement a system to promote alternative political parties. So that their ideas can be introduced into the current system. The Libertarian and Green parties, for example, need to gain more ground on the political field. John Adam's once said that the greatest threat to our republic is a battle solely between two political parties that are completely opposed to eachother. He was right.
I agree with you and have always advocated same. My proposal at least forces challengers from each party to come up with better ideas in order to oust the incumbent. It also forces the incumbent to work harder for the people since, theoretically, it is their vote that counts.