I don't understand why you think you're paying for them to advertise to you. Do you ductape the logos of the Pepsi you drink in public, or if you had an awesome time riding rollercoasters in Six Flags do you keep it to yourself and tell no one because that'd be advertising? I can understand not wanting to support a brand like Nike. They make their products cheaper and sell them higher then many off name brands. It's not so much the advertising as it is a ripoff.
Just because a product makes you want to buy another product doesn't mean it's an advertisement. I buy Sequels to games I liked. That doesn't mean the first game was an advertisement. It had value in and of itself, The same goes for the Spore Character creator.
Honestly, I wonder how much money they are making considering the full Creature creator is 300MB, the Trial version is 200+mb and they're maintaining a free site to host everyone's uploaded creature. I'm SURE they're making money with it, but isn't that the whole point of developing games in the first place?
For anyone that cares I have a few creatures uploaded at
http://www.spore.com/sporepedia#qry=usr-cmike1