I consider it dubious because 99.9% of consumers don't get a new credit card every 3-6 months as required by your schemes.

Also, the 20,000 for $750 seems ridiculous to count toward CardIt because there are a lot easier ways to rack up to those $750 minimums, such as everyday spending. Personally, I would only count miles I would not have earned otherwise, and a signup bonus does not fall into that category.