While you may be able to get a room only discount (nothing to do with land/sea), I would consider how many hours you'll be spending at the resort. If your plane gets in earlier in the day (say 11am), then I could see enjoying a WDW resort the night before the cruise (you could use the pool, have dinner, ride the monorail, maybe catch fireworks from outside the park). If your flight gets in later (say 7pm), I'd stay closer to the airport at a hotel with a free airport shuttle - sort of a sleep and go situation.
Back in 2011, I flew in 2 days before our cruise - our flight was to land around 6pm but there was a bit of delay and we landed about 8pm - by the time we got to the resort on Magical express it was 9:30pm. Thankfully we still had a full park day the next day but if it had been the day before the cruise, I would have been kicking myself for spending the extra to basically just eat and sleep (and of course no free breakfast at WDW like many of the airport hotels).