Scrapping Missile Bases: Yes, you can do it! Select the planet with too many missile bases. Press 'B' and you will get a slider asking how many bases you'd like to get rid of.
Why? So you don't have to pay maintenance on those bases any more. Useful for planets which are no longer near enemy lines. e.g. after you've wiped out an isolated race.
Seeing attacks coming:
Improved Space Scanner and Advanced Space Scanner open up a new feature in the interface. Pressing F8 or F9 will now step you forwards or backwards through all the planets that you control that are the destination for an enemy fleet or transports. You need never miss an incoming attack again!
Relocating ships: If your ship-building planets are all set to automatically send their ships to some other planet, you can change them all at once. Select the planet you'd like the ships to go to, and hit Alt-R. All your blue relocation lines will point to that planet. Of course, in a larger galaxy it'll take ships several turns to get there - and the ships already on their way to other places will keep going. This is no good if you need local arrangements for different purposes - but if you're in a macro phase where you just want all your new warships to head for the field of combat, this is a good way to do it. If you use Alt-R while on a planet that is currently sending its ships elsewhere, it will stop sending its ships anywhere.
F1: Help key. Shows a basic tutorial explaining each screen
F2: Cycle forward through planets. Planets cycle in order of listing in Planets screen
F3: Cycle backwards through planets
F4: Cycle forward through garrison fleets
F5: Cycle backwards through garrison fleets
F6: Select Planet's Fleet (including no fleet)
F7: Select Planet's Fleet (including no fleet)
F8: Cycle forward through threatened planets
F9: Cycle backward through threatened planets
F10: Save game to Auto-Save slot/Continue Game slot
B: Scrap Missile Bases
C: Espionage report (Spies caught this turn)
G: Open Game Menu
D: Open Design Screen
F: Open Fleet Screen
R: Open Races Screen
P: Open Planets Screen
T: Open Tech Screen
N: Next Turn
Alt-C: Center map on selected planet
Alt-M: Show 5x5 parsec grid
Alt-R: Redirect all waypoints to the selected planet
=: Only in Tech Screen. Sets all research to the same level, regardless of slider locks