I would rather spend more money on widening the 101 freeway or building a new one rather than spending ton of money on Caltrain doors.
In the case of this particular "101", that point is not yet met. However, when the cost of 6.4 miles of single-lane is $72 million, it does get a bit pricey. [1]
They are planning to add another TOLL/HOV lane for most of the corridor, and open up the existing HOV to TOLL. You might get to drive it in 2018! But I don't see cost estimates for that one yet. [2]
[1] - http://www.vta.org/projects-and-programs/highway/us-101-auxi...
[2] - http://www.vta.org/projects-and-programs/highway/us-101-expr...
/joking, obviously