I believe the supports are the same size. They just added a second arch to add more support to the towers.
The towers were reinforced and stuccoed in 1914. This was due to weakening of the base of the towers by the 1913 flood and the increase of heavier vehicle traffic on the bridge. So, they reinforced the towers, put in a new deck and replaced the original cables to make the bridge stronger - and so it could accommodate automobile traffic. (The City of Waco had also discussed complete replacement of the bridge around 10 years earlier).
I always thought it would be cool to restore the towers to their original form, especially since the bridge only accommodates foot traffic now, but that probably involves too many permits, too much cost and would step on too many toes - because everyone who remembers the bridges in their original form is no longer with us.
"Smarter than the Average Bear."