Greece set records elsewhere, but Mykonos and Santorini moved the other way. Air arrivals fell sharply in the first four months, then recovered through last-minute bookings and price cuts of up to 50 percent. Cruise day-trippers crowded the streets while overnight guests spent differently. Luxury hotels held rates; many others did not. Dining felt the squeeze first. For the first time in years, the island has to prove it is worth the price.