The banana skin is cool, but I already have Celestine Soraka, and I think that's fantastic, so not getting it.
All in all, I still play her sometimes. I build more or less full AP, for the best healing. Movement speed is also very important to have the positioning you need as Soraka. You need to be at a safe distance, but close enough to heal when you need to, and in range of Starcall, and to drop Equinox at just the right time. It's a delicate balance. I do run flat HP/5 Quints, which do wonders for your health sustain. It's just so satisfying to interrupt an enemy jumping on your ADC with Equinox, burst heal with Wish, and then heal up to full HP in just a few seconds with a few Infusions. Her healing is just insane, and with AP, you don't have to burn as much of your own health to do it either. If you want to be safer, GA and SV, and the rest as full AP.
And its fun because a lot of people underestimate her, or do not understand her matchups. I FIRST PICKED Soraka (I was in a "FK IT!" mood), and the enemy counterpicked with Katarina. And I'm like... do you not understand that combo casters get wrecked by Equinox? It's such a safe zone for your team. Learning how to use that properly will make or break your experience as Soraka.
Anyway, as for hitting Starcalls in lane. Try varying how you are using it. Also weave in Autoattacks. They will be looking for the Starcall, and will let you get in range for a banana, or they will let you zone them away from creeps. When they adjust to that, then you hit them with a Starcall. It's all in the mindgames.