We just returned last week. Arrived and departed via Delta (Winair rt to SB). Our experience - arrived on a Monday - had VIP - skipped every line and didn't have to think about anything until we arrived at the gate. Our flight was on time and although VIP service tried to get us on earlier flight on Winair - they were all booked so we sat and waited 2 hours at the gate for our scheduled departing flight. The VIP service obviously left us to wait alone as their services were no longer needed. If you ask me if this was worth it, I would say it was a very nice perk to get off the plane in SXM and be escorted through the many lines and also not to have to retrieve our luggage and recheck. Since we did have 2 hours, it would not have been an issue, just a lot of standing and waiting.
On return - I did not book VIP as I was less anxious to get home than I was to get to SB. We had 2 hours again between flights so standing through the lines was not an issue. Our next trip - I will likely book VIP both ways and schedule tighter flight connections.