It seems like at least some of this information should be on the board. Players should't have to collate information from the board to a chart or to the players cards.

My first thought is small colored bead in player colors. When a player takes a card he places beads on each city named, so he makes the board. Then the cards have no more use, and can be put in the box. All attention can be focussed on the board. Since you can see not only where players' links are, but also where their city interest lies, you can make much more informed decisions.

Perhaps wooden disk stacking to eliminate the clutter factor? You could return other players disks once a city is claimed (an put the player cube on top of it)?

As for cost, how many disks would one need? I'm going to guess somewhere in the 20-30 range? On B&B, they're going for $5 for 24. So $25 to support the game? Hm.