Got my son-in-law's Space Mission working last weekend after working on it for a few hours every night for a week. It's a pretty fun machine and has a lot of features to it. Since I have a Fireball EM and El Dorado, Space Mission's spinner is lots of fun.
I'm waiting for my order from the Pinball Resource to arrive and I have a few minor repairs to make this weekend. New flipper bats and a new Lock Relay Coil. Should be able to move the machine back to my daughter/son-in-law's house over the weekend so they can begin enjoying it.
As far as game strategy, all I can figure out is that it is a good idea to hit the swinging target to light up the game features for double bonus, light the spinner for 1,000 a spin, and try to get an extra ball. The trick seems to not hit the swinging target after that so the features stay activated as long as possible.
I really like the 100,000 score lights for when you roll the score reels over. My Fireball, Time Zone, and El Dorado do not have that feature. Getting extra balls is fun too. I also get a kick out of making the knocker go off to award credits based on high scores and the after game match.