By your logic, BuyDomainNamesForSaleByOwner.com would also be worth getting because "for sale by owner" is a good phrase and is in it. So too would BuyAWebsiteDomainName.com. Adding length to get an extra phrase rarely if ever works, especially if the phrase in question is already 3+ words and are not that valuable. Length and extension will always be factors in this business, even with SEO being as important as it is.
Just because 1 or 2 good phrases are IN a name doesn't make the name itself a good phrase, and unless you're going for brandable names, your name really needs to be a good phrase in and of itself. SearchEngineOptimization.com is a perfect example. Despite its crazy length, anyone here would like to own that name, because it's a popular phrase. However, "buy domain names for sale" has 0 OVT, and "buy a website name" has 173, sharing it with "buy website names" and thus not really being good for its length. Google results show too...9,760 for "buy domain names for sale", and only 28 for "buy a website name", both unimpressive, and especially not good since you're competing against the length of the names.
You're obviously going for generic names looking for good SERPs, and who knows, you may get it. However, names like that have absolutely no resale market IMO unless you've got a page developed that is reaping the benefits of the SERPs, and even then, you probably wouldn't be able to sell for that many months of revenue because the names are much too long to be business quality. Keep in mind also that on the SERPs, you'd have a much longer name in competition with established domain sites with much shorter, more professional sounding names. Maybe you can prove us wrong and get a sale out of it, but my appraisal is reg fees, and I apologize in advance if ownthisdomainnow doesn't like my appraisal!