Right, closing at .30-.40 is a good place to exit, BUT you also want to consider that remaining 2140/2150 will be accumulating more short delta if SPX continues higher. With that in mind you can consider:
A) Closing 1830/1820 and waiting for a pullback to sell a new spread or
B) Closing 1830/1820 and selling a new spread for about a .90c credit or
C) Do nothing and try to exit the whole thing at 40-50% of original credit.