So basically you’re talking about catching both planets when their orbital velocities are at their optimum for speedy transit. I was looking at proximity alone.
I guess if I were a billionaire with an interest in space I would either get on board with asteroid mining or look into building a base on the moon. Faster more efficient propulsion systems are also a good thing to put money into.
I’m all for going to mars but believe that if you can live on the moon, you will prove the ability to live on mars. The moon is a far harsher environment to live in than Mars. Mars isn’t a hard vacuum, the temperature variations aren’t as extreme, and the planet does offer at least some radiation protection. On the downside, Mars is a long way away and its a lot harder to get off the surface once you’re there. I actually think the Russians are on the right track in concentrating on the Martian moons.
In Kim Stanley Robinson's novel Red Mars, the first eight human settlers agreed to make a one way trip - to pave the way for future expansion missions. The future missions came - but there was always a chance that due to wars or budget cuts they might not have.