The questions of whether the exclusive use of gold coins in space is a limiting factor in space trades is an interesting one. The way I look at it is to compare the gold coins costs in space to what the player market values a gold coins at in SC$. Given that I sell electric power, per coin, in amounts that would readily earn me $180 billion in the game, that seems to be a fair estimation of player value of a coin.
Looking at space prices, you would have to ask yourself:
1. Would you pay $2.16T for 25 nuclear missiles instead of 12 coins (the cheapest price currently offered in space)?
2. $360 Billion for 25 stealth bombers instead of 2 coins?
3. $1.53 Trillion for a mobile interceptor wing instead of 8.5 coins?
Currently, it seems the smartest thing to do is to complete these calculations for yourself and figure the smartest use of your coins. If you have the cash, you can make many of these items on your own. If you have an abundance of cash, you could become a seller. Newer players who have a bunch of game level and war level awards ahead of them and often find an easy path to ranking awards, having no score penalty, are often much more flush with coins than cash and are natural customers of the space market.
My analysis is that the currency does not have to be much of a barrier. A bigger barrier, in my view, is the cost of being in space in the first place. I think docks should cost 100 coins, instead of 200, and all current owners should be refunded the other 100. Those prices seem more in-line with the utility of space.
As to the price of mobile units specifically, the lower prices seen months ago were driven by sell-offs of long-ago produced stocks. Some accounts changed hands and some assets were gained with the conquering of other player assets. New owners of these assets, looking to gain quick coins, sold some of these assets below the costs of assembling new units (indeed, I was sometimes a buyer of these). The prices you see now reflect a similar cost of producing a new unit, weapons/ammo/upgrades.