When the parking lot at the transit stops are overfull, it's clear that people want to be there, so they might want to live there. But keep in mind that the caltrain lots also backfill for not transit parking -- event parking for SAP center and parking for Sunnyvale downtown.
If everybody drives 5 miles and parks at the transit stop, instead of driving 15 miles to park at work, that's a lot less driving.
When the parking lot at the transit stops are overfull, it's clear that people want to be there, so they might want to live there
I don't think that's necessarily true - there are lots of transit stops (even busy stops with busy parking lots) in areas where I wouldn't want to live.
If everybody drives 5 miles and parks at the transit stop, instead of driving 15 miles to park at work, that's a lot less driving.