Sure, Rafe had his own agenda, style, and purpose for how he adapted the WoT. Any showrunner, director, producer does. To be honest, I don't think Rafe is that clever.
The simpler answer is likely what @bringbackthomsmoustache pointed out. Centuries and more of low tech heating easily explains the dinginess of the ancient tower. The Aes Sedai could easily 'scrub' the walls white with the Power to a gleaming surface. I could accept that, but I also accept that showing the tower's age with some grime speaks to its permanence.