The answer to some of those is complex, whats the target platform, because windows.exe or flash makes the most sense with the current control scheme, there isn't a lot you can do to change it with the two player mechanic.
I would either increase the missile speed or make it autotarget the nearest enemy, my issue with it was that not only does it take some time to fly to where you want it doesnt seem to do a terrible amount of damage when you get there, I do get that it has to fit in with the ship pricing, and shooting down a 3p ship with a 1p missile would be a little broken.
I do like the satisfying pling noise, I'm a sucker for a good pling.
I really like the sattellite power up, I'd like to be able to buy those?
If the remote missiles main function is to fly around collecting coins, perhaps some sort of dedicated resource harvesting unit might work better?
Why do bullets kill coins :p seperate them to a new group? I wasn't actually sure if the coins were dying or being collected.
What I would do if it were my thing,
increase missile speed by 2-3 times.
Make the smallest unit fly to and collect coins, before attacking enemy ships/planet.
Remove the down arrow as the buy key and just have it for menu nav, and make a new key for selecting.
It is however not my thing what i made innit, and I like that it's not like a gazillion other games I've played, but it does need a little rejigging.
And glad you liked drone ring

So did I.