Buck's is a pretty nice place and the food is actually quite good. Far better than SF's deal making hotspot, the Creamery, where parking is also hard to find.
Besides the usual arguments against public transit, such as schedule inflexibility, comfort, and cost[1], there's overall trip time.
Unless your other endpoint is similarly close to a Caltrain "bullet" stop (and one is taking such a "bullet" train), driving takes less time on a typical day (and always during any off-peak period).
[1] Primarily for ad-hoc trips, and especially acute for dual-occupancy cars. For two people, Lawrence Caltrain to the Creamery would cost $19 more by train than incremental cost of driving. (Ignoring parking costs.. which, if more than $24.50 near the Creamery would, indeed, wipe out the savings).