I always try to take advantage of AP utility scaling on supports. Once they get a couple hundred AP, supports have terrifyingly strong utility, heals and shields.
It's the exact reason I'll never understand people building Soraka tanky. I realise her peel is mediocre but Jesus, you might regenerate your HP a little better with tanky items but who cares when you'll spend a lot less health for the same effect on AP Soraka, and you'll heal much more with your Starcall too.
That said, supports could use better AP itemisation. Ardent Censer especially could use a buff to like 60 AP. At the end of the day you probably shouldn't be buying Deathcap on a support, you're basically a poor man's AP carry at that point.