Not to mention they have (probably) changed it. Instead of getting 10 levels for every maxed profession, I only got about 5-6 levels max with a booster activated. I don't know when they've changed it, but when I was trying this last month, I couldn't reach 10 levels a single time like everyone was screaming.
So it's only worth it if you have 1. too much money or 2. a lot of stuff gaining dust in your bank.