"But it seems our billionaires are boring old farts who prefer to play it safe by buying properties."
To give him his dues, and it pains me to say this, Richard Branson is investing in technology projects. Sadly it seems that his vision is a little restricted though. Musk and Bezos are clearly enthusiastic and have been steeped in The Culture as well as culture. Those two want to make our future like the ones we saw in old re-runs on Saturday morning Kids TV. The world of "Lost in Space", "TinTin", RKO serials and "Flash Gordon" where rockets were infinitely reusable.
Branson's ambitions are more modest but have the potential to pay off in slightly unexpected ways. So there's Virgin Galactic which isn't much more than a way of separating millionaires from their cash in return for an experience which used to be possible from Thunder City - an edge of atmosphere trip. White Knight 2 and Spaceship 2 have other potential uses for lifting loads for sub-orbital missions at low cost and given the lift capability of WK2 it could be used to lift a two-stage payload that could be fired into orbit.
Branson's other project is his investment in Boom, which is planning a small (45 seat) SST. I hope that comes off also.
The shame is that these are US projects and an investment in Reaction Engines would be an investment in UK engineering.