This is a controversial question.
If you are thinking about what Marcus call "Click flopping" with Adsence, then you might what a new/different domain. Cick flopping is where you have one website with low searches and competition so you can get good ranking in the search results pages like google and Bing. - The same basically for PPC, you don't want a lot of Ad competition either.
So on the first sight you have no Google Adsense and remember you don't use the high search/competition keywords on this first site. But you put links on this first site that will flip them to a second website (or more) with all the high search volume and competition on these other sites. - It's these second site that have the high clicks payout to you.
Now you could try creating sub-domains which are independent website, but are attached to your primary domain. These subdomains can have totally different theme layouts. - you treat them link a separate website. The only disadvantage is that your primary domain name is attached to the sub-domain.
An example say you have a domain name of Animal.com and on this animal site you talk about cats and dogs. You can then create a subdomain for cats and one for dogs. So the one for cats would be www.cat.animal.com - note the primary domain title in it. And the one for dogs would be www.dog.animal.com
I hope I covered your question. So for you, you might want to try the sub-domain method first, because it is "FREE" and see what happens. You can always latter buy domains in the sub-domain doesn't pan out.