Much to my surprise, Bean spends far more time on their kitty tower than Wylla does. You can frequently find her on the third tier, where she looks out the window surveying the world below, or naps. She spends so much time on the tower, she's taken on a subtle "new carpet" smell.
Wylla does use the tower for scratching, and will climb to the top for safety when the girls are chasing each other, but it's rare to see her hanging out there on her own. If Wylla wants to perch, she'll find herself a human.
Even though Wylla doesn't use it as much as I thought she might, it was worth the investment for Bean alone. She enjoys her tower time.