I'd want to keep mine for parking and discounts - I know you can add parking to the Flex, but we also spend enough $ there that between that and the discounts, we may as well keep one Signature. I occasionally go with friends, or I meet friends at DTD and pop into the parks after, solo - I definitely go the most of the three members of my family, and I'm more likely to go last minute during the evening with a friend, so the reservations might hurt me there.
A few years ago, when I still worked, my husband and I were Deluxe and our daughter was a Signature! We figured whoever went and needed parking/discounts would always take her, so she had the best pass.
Honestly, we'll probably all just end up staying Signature... my husband will just decide he doesn't want to be constricted and will say things like, "I work long hours precisely so we can afford things like this, remember how annoying Blackout Days were?" and we'll just keep it as it is... but for two passes, it's enough $ to at least do the research and consider it!