If a centralised system is desired, no blockchain is necessary at all.
Earth does not have any such timestamping restrictions on blocks.
It is not "desired" - it would only be necessary in the unlikely event of a massive attack from Earth. Something we could discuss for the next 10 years to figure out. How to best address.
Higher supply decreases value, not increases it... so this doesn't really argue why it should be increased quicker.
Psychology: "Oh no, all Marscoin will be gone by the time they leave". Vs. "Oh, they have 100 Mio. Marscoins of which only 30 Mio are mined on Earth, who cares, my grandchildren can mine on Mars".
Well, now it sounds like the goal is a centralised system masquerading as a decentralised one...
I'd be more inclined to support a system that improves on Bitcoin (or at least retains its functionality) rather than seems to be introducing new problems without addressing the existing ones.
Welcome suggestions how you would implement such a system, initially, when Mars mining server are week and hashrate on Earth is high. So far Marscoin is completely decentral and if we can keep it that way, the better. Check out
http://mars-project.com for discussions on this topic and/or the Marscoin IRC channel.