Going to be at the Paris Westin this weekend and am weighing the ParisVisite option vs. just paying the RER fare from/to CDG and picking up a carnet.

Since I'm never sure how much or little I'll use the metro in Paris normally I just do the ParisVisite 6-zoner, but since there is no 4-day option I am weighing options this time 'round. And it seems to me that the CDG RER return is €16,80 and I could pick up a carnet for ~€12.

It frankly has me thinking that I've been throwing away money on the three-day parisvisites in the past.

Am I missing something?