Please think of these as a mini-expansion or stretch goal. They are not necessary to play the game otherwise I would have included them in the standard game.
In Keyper you can score points in various ways. So an example of one of the extra tiles is that you score points for the number of female keyples in your team at the end of the game. This would not have been appropriate in standard game as the basic keyples are all the same except for their colours.
My aim with the character keyples (and tiles) is simply to enhance the overall game experience. A number of gamers have commented, for example, that Keyflower has been a successful 'spouse' game for them. I think Juliet's art style has contributed to this and know that Vicki will do a great job also. I think the character keyples will increase the game's attractiveness in this respect also. And Keyper is a similar game in structure and player interaction, although the worker placement mechanics are very different.
Another characteristic of Keyper, which is mentioned in Alan How's quote, is that Keyper is a very inclusive game. In the multi-player game especially, you are encouraging the other players to work with you as opposed to games such as Keyflower, where you are bidding - in conflict - with the other players.
There are certainly opportunities to upset your opponents. For example when they have no keyples left and are laying down their keyples, at which point you play onto their board onto a field which is producing something they don't need. They may then have to 'lay down' that keyple if there are no alternatives. They will still gain the resources and the keyple, but perhaps not what they were hoping for.