Make Notification More Prominent
I was hoping that the Accessibility preference combined with Notifications sounds would induce a screen flash but it does not...

However, have you looked at using Growl (for notifications) and OmniGrowl (specifically to enable iCal notifications)? This is good if you mainly want iCal notifications (doesn't work with a lot of other apps) and especially if you'd like to have a more notification-based desktop including other apps and want a more granular level of control over how your notifications appear to you. Growl has a lot of nifty other things it can do that can help with and it's super customizable.