Buy and hold rental properties are good, if you're looking for an alternative income stream. Start flying more and stockpile a lot of cash. Keep your credit score up and wait for the next real estate bust. (it's going to happen). Then, buy inexpensive homes (3-4 bedroom) in blue collar neighborhoods. Fix them up a little and rent them out. You have to maintain them and put up with the occasional loser, but you basically end up with other people making your investment for you.

I've funded my retirement aggressively in the stock market for 30 years. The real estate is worth more. Only do it if you like it, because the reality is that you probably won't need the money (especially if you keep your first wife). If you save 10 percent of what you earn and burn the rest on having fun, you'll probably enjoy your life more.