Lots of great advice here so I will try to add some meta observations that may help you along the way. The fact that you mention "working your ass off" and trying to build up something big so you can sell it in 10-15 years tells me you just may be the type of individual who will actually, you know, make it.
1. Forget these peole throwing brands like Apple, Amazon or Google around. You (chances are) will never get to be an Uber or Starbucks so don't set yourself up (emotionally) for failure.
2. With porn, in today climate (2015), it is virtually impossible to create a GIANT mega-brand like a Naughty America or Brazzers. The entire Industry has shrunk and consolodated to the point where many sites is basically the only way to go (my personal business model). But "mainstream"? Theoretically limitless.
3. You are going down the right road, doing what you are already doing (another reason to support your efforts here). Test out 10 things, see what sticks, ramp up those. Rinse/repeat. So here's my two cents on this: keep going! What will happen is one or three or eight projects will emerge as the real moneymakers. This may be after you try fifty things! But if you keep going and then follow the money - and put most of your efforts there - you have what you are trying to do (build something long lasting). It WILL take time to test out all these things, build your sites, try different marketing techniques and test out different traffic sources. But I honestly think it's the smarter way to go.
4. You already have your answer. Not to sound like Star Wars here but search your feelings (Luke?). LOL IF there was one burning idea blazing away inside your soul you would KNOW that's the only thing to focus your passion on. But if you don't feel the drive to build one mega site then that's telling you nothing has caught your spirit yet. But that's ALSO "good news". It means you're about MAKING MONEY, whatever the product or service may be.
5. Never, ever stop. I mean you CAN of course, if you want, but then the game is over because YOU stopped playing it. You have experience and some traction now. Give yourself a reasonable time frame and a reasonable financial goal. If you don't hit it - or even come close - time to do something else. But if you are inching closer every day....never, ever stop.
Best of luck to you and your endeavors!!