I think the subject is interesting. A first step would be to collect samples of different Tower cards.
One of the most fascinating things, is that possibly the Tower originally was not a Tower.
See for instance the
Charles VI / Gringonneur Tower. As far as I know, this is the most ancient existing Tower card (Florence, second half of the XV Century), and to me it looks more like the gates of a town than a tower.
In ancient times, that card was not known as the Tower or la Torre. In the
Sermone de Ludo cum Aliis (1450/1480) it is called "Sagitta" (i.e. arrow, but could also mean lightning). In the Merlin Cocai sonnet (1527) it is called Foco (fire).
Moreover, the Minchiate "tower" seems to represent the
Expulsion from the Garden of Eden (I don't know how ancient this version of the minchiate image is).
So I would like to know when and where did the tower become a tower?