Curious for your thoughts: currently, fares from LIT-ORD/DEN-SFO/SJC at an ideal time are hovering around $450 for next Sunday (6/4). If I take an early morning flight to SJC, however, I can book W at $285. A more realistically timed, but still early, flight to SFO books into W at $295.

Is it a reasonable strategy to book one of these flights in hopes of the same fare class becoming available for a flight later in the day (closer to the ideal time)? Some nuances that may affect this include:

• Destination airport must remain the same, but anyone know of SJC SDCs auto-searching for SFO as well (this happens unprompted with general fare searches)? I know agents can sometimes support with near- but not co-terminal airports, but wondering if the system will automatically expand the search day-of, eliminating that extra step.
• If only higher fare classes are available day-of, do Premier members actually get charged the full fare difference? I've seen on a number of flights before that all changes were near $0, but that might be because I usually fly higher fare classes for work.

As of now, I see W availability into SJC at the ideal time and loads of H-adjacent availability into SFO, but I know things could change dramatically in a week. Curious to hear your thoughts, and thanks in advance!