The good thing about rewards is that you can limit them to a certain number of backers, so Playtonic could easily offer, for example, a signed and exclusive look at a character or level design before anyone else. People might find that special and offer a lot of money (then try to sell it to the media
). It doesn't cost Playtonic much to share their doodles, so the profit is good here.
They could also offer a limited amount of people a shortish Skype chat in which they can discuss the development of the old games, secrets like Stop 'N' Swop and the upcoming project, scheduling the chats on a certain day as to fit them all in. People might pay good money just for their time.
I think Playtonic should really take advantage of their history and who they are: legends.