I am also adding Z brush to my tool box, but is a much longer learning curve than Aspire.
I have at least 150-hours of training videos and then numerous hours of online sites that I watched to learn ZBrush. That's not counting the many times I've had to go back to a video to remember how something was done. I think I could've learn how to fly a Boeing 747 easier. Weekly, I get emails of ZBrushLIVE streaming digest that give me many artist's workshops, showing hours of new training techniques, which also aids in the learning process. Believe me, Aspire is much easier and I use that software more than anything else. I been using Aspire since it came on the market and I think the Double Sided feature is the best upgrade yet. Gary