I suggest for every year you have held a planet, Each resource will go up by 1 point, also for each 3 (or 5?) the size increases by 1 point, up to a cap of X15/VM. This will show that a planet under your control slowly flurishes and improves. overtime people are always trying to inprove what they have. Currently that would AT BEST be +5 terraformers and +1 quasi. If a planet is invaded/changes hands ect the timer resets.

Would that mean that if a planet were invaded that it would revert back to its original production and size? Would only seem fair. Could be done if it were added as an event but still would be a bit confusing when the planet you end up with isn't the same as the one you invaded.

Overall I'd say no. Your "AT BEST" of 5 TD and 1 QSE does not take into account that those are PER PLANET and PER PLAYER. When multiplied out that's a heck of a lot of TD/QSE given away. I would much rather see more ways to get a planet above the 15x point for all 3 resources.