There are signs up all over Granville Island asking you for feedback on some planned improvements. They direct you to www.speak-up.ca, which has an online feedback form you can fill out, along with lots more information about the changes Granville Island is considering.
I filled out their feedback form, and here are my extra suggestions:
More maps and sign-posts everywhere. It's way too easy to get lost there now.
Better public transport connections. How about a bus that actually goes onto Granville Island?
More nightlife. The fringe festival is a great example of how hopping GI could be at night. Keeping 1 aquabus going later into the night would be helpful here.