Yup, Starcall is a great skill to have.
If anything, I usually leave her healing for later on. Most people do stack ways for them to survive a fight already, so it's usually the last thing anyone will need. Lvl1 gives the same armor as Lvl5, and so Lvl1 is usually all you'll need till mid game.
I usually prioritize Infuse, since it's the largest mana return this game has to offer. It's also Soraka's exclusive ability, and her only CC (silence). She also never need any mana item as long as you keep Infuse maxed out.
I usually get 1 or 2 (or up to 5) early kills with smart use of Infuse and Exhaust. Learn the limit of when to use it on yourself, your friend, or your opponents, and it easily becomes the best spell in the game.
As for stats, I prioritize CD reduction. Soraka comes built in with MR and AR (passive and Astral Blessing), which makes her quite tough for a healer. Scaling on anything but Wish is relatively poor, and you get a much better return from CD reduction--especially since it means you can heal more often (or keep more friends buffed with extra armor), put up Starcall debuff much faster, and also Infuse a lot more. Short CD means you can afford to pop one on the enemy, knowing that it will be up again for you to use very quickly.
ps. A 1.6 sec starcall hurts a **** ton even with low AP.