Kia - the color enhancing conditioners are good, but I have better luck just using a rinse on top of my colors to extend their life.
You can do the trick you talked about - color, developer, conditioner - but IMO you shouldn't do that any more frequently than you would semi-perm color. As long as there's developer in there, I'd limit the use to once every 2 months. No more. /images/graemlins/nono.gif
A RINSE, you could use once every 2 weeks if you wanted to (watching for buildup)....I have.
BTW - Redken makes fantastic color extending products. /images/graemlins/smile.gif