The pro control is a nice unit, I think having an edit pack is more useful than 3 fader packs myself, but it depends on what you're going to do with it. Clients tend to be impressed by large consoles, especially when they see the faders moving around.
The most interesting thing to me is how low the price of the used pro control has gotten to, and how high the price of a used control 24 has remained.
I think you need to put a value on your time to justify it. If you're going to keep your current PT rig for a few years, and you have enough work where the pro control will save you time, then it makes sense. The other reason is the wow factor with your clients, who I doubt will care if it doesn't work with pro tools 9.