Would you pay to post good content on a site relevant to your audience that has good domain authority to boot? Depends on the site and depends on the content.

We don't charge our guest bloggers (yochicago.com), but we vet them pretty heavily - they need to contribute something to our audience.  But we do blog on behalf of sponsors - and since we're doing the writing - it's always relevant (to some degree at least).  Our readers comment on our (clearly identified) sponsored content's relevance occasionally, but generally understand that someone has to pay the bills.  It's a pretty effective means of advertising / editorial / authority-building in one.

I could see paying to guest blog on the right site as being more effective than starting your own under certain circumstances.

Given that pages are viewed independently of one another, the only consistency that matters is if you're consistently using keyword strings that would tend to surface for the broadest range of queries 'remove chocolate stains'.  That said, competition may require that you get more specific, i.e., 'remove x stains from y'.  Consistency will make it easier to test and get a feel for what works over time.