For mpex to be worth 1 million btc @ 30% apr it would need to increase profit around 50000% compared to last quarters.
See, there is your problem. Why do you think an investment should earn 30% apr? Especially when it is measured in bitcoins, which tend to be deflationary anyway?
Because you need a higher than average apr to accomodate for the ridiculous registration fee. Otherwise it wouldn't be an intelligent investment, even if you overlook the fact that its basicly a pyramid scheme.
Edit: That means that a $100k (125BTC) investment
needs a (roughly) 30% apr to get back the registration fee. No satoshi earned here. Just to make it clear.