Here are my suggestions for planet raiding and hacking:
In order to raid your crew has to be greater than or equal to the current planet population.
The chance of a successful raid is based on your crew size vs planet population. If bother are equal then you have a 50% of success.
For hacking the chance of success would be based on scan vs planet cloak.
Each planet can only be raided/hacked once an hour.
The reward for the raid/hack is 10% to 50% of the planets hourly production of artifact points, mineral points or research points.

I believe these rules would give a decent reward without decimating the target player. It would also make the planetary protection artifacts more useful.

As an add:

Planet raids should have a 1 hour cooldown timer (to account for the success bonus being only for 1 hour in advance) The invasion defence vs invasion attack should count in raids because many of the modules and ship buildings that grant those bonuses make sense in raids. (like the soldier outpost)
success: gain the planet's next production as your own
critical success: same as success but lowers the planet's invasion defence for 1 hour
failure: deals damage to player's ship (as the ship is repelled by the planet's defences before it could land)
critical failure: same as failure but increases the planet's invasion defence for 1 hour

Planet hacks should work differnetly, as research is stolen in a raid (by stealing the data file discs). I think planet hacks should directly influence the planet's stats, like corrupting satelite jammer frequencies to lower the planet's cloak or altering shield modulation to lower the planet's defense.
success: lowers 1 random planet stat by 10
critical success: lowers all stats by 10
failure: a counter-virus disables your ship computers, so you cannot hack for 2 hours.
critical failure: a counter-virus shuts down your ship systems, giving you +1 truce and no hacking for 6 hours.