Elizabeth2 and Enchanted wrote on my wall recently that they had read this post. It has been so long since I wrote it, that I wanted to go back and read it again. Here are some updates, since the game has changed since its release April 2011.
(1) there are no more Mastery items. They used to be a gift from TeamLava when you made enough of an item that you progressed from level 1, 2, 3, and 4. They were dropped in an early patch.
(2) Experience through purchasing items in the Design mode: Every item you buy grants experience. Items that cost gems grant a lot of experience. Expanding your shop grants a lot of experience. I am SO thrilled with the new expansion options. I had been bored with the game enough to stop playing for a few months (what do you do with 12 million gold?), and now I have new goals to strive for.
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(3) Popularity: the wall mirrors now count as real mirrors, so don't block with with tables or decorations and your shoppers will now go look at themselves in the wall mirrors.