Many players use the sweep option for towers now.
Perhaps you can use a newer random map generator to create towers that are more of a puzzle. If they get frustrated trying to solve it, to get to the top they can still use the sweep option. There could be a bonus for not using sweep.
(Some random configurations might not have a solution. You may have to sweep just that floor.)
Also skins. It has been mentioned before to skin the towers to their locations. This could be included in the new random map generator.