If this is your only chance to see KL, then absolutely spend the night in the city, GH or not. At that landing time, you'll have plenty of time to see the bustling street hawker scene and get some great food or go see the Petronas Towers or both. I love KL but one only needs 1-3 days in KL anyway so take advantage of the time.

Costs? Nothing if you can afford Alila Maldives.