I believe that the VL should get some sort of an incentive to go full mobile (IE stripping the capital and the rest of your core worlds) 

Here are some basic ideas:

1) Vorastra gets a HP/Armor buff when you have 0 planets under your control.

2) Culture repel rate of capital ships is increased by 100% when you have 0 planets under your control. (nice synergy with STTC)

3) Spawn Phase stabilizer ability cool down is reduced by 400% when you have 0 planets, summon dark fleet cooldown reduced by 400% when you have 0 planets under your control.

4) Get 50% more from stripping your own capital (It's the point of no return)

To counter this, I propose the following changes: Which would be activated the moment you research STTC.

1) STTC takes 50-100% longer to strip and it's income is taxed by fleet supply UNTIL your capital planet is stripped or if your capital planet is being stripped or if  the Vorasta is your capital, at which point it goes back to the current settings.

2) All VL Population growth is linearly reduced as the game goes on until it reaches .1 or so, this is to give them diminishing returns the longer they choose to be settled.

3) Diminishing returns on Crystal and metal extractors.  (same idea as above), extractors get less efficent as the game goes on.

3) A negative multiplier when defending your own gravity wells, and a bonus when you are in hostile gravity wells.