This is something Ive been thinking about for a while now. There is really no incentive to completely strip all your planets and go fully mobile. Besides bodging novalith rounds and being able to avoid combat most of the time i cant really think of a good reason. In fact there are many reasons to keep several of your planets.
1. Kostura cannon. If you abandon all your planets you lose access to the most powerful super weapon in the game. Even more so when combined with the VL titans ability to summon phase stabilizers and summon several ships. You could assault an enemy planet deep in there territory and instantly reinforce your self while at the same time launching an assault from outside their territory forcing them to fight a war on two fronts.
2. 2 capitals are better then one. Especially on the capital victory setting but even without its still useful to keep the increased tax and resource rate provided by having your cap.
3. Steady income. While STTC provides a large amount of income its not steady there fore if you get caught in situatuon where you cant rapidly advance you completely lose your source of income.
4. choosing the ships you want. The summon dark fleet ability's of the phase stabilizer don't let you choose the ship you want. therefore if the enemy is spamming one particular type of ship you can spam the counter or you lost alot of one particular ship in one battle you can simply build the ships you want.
5. Culture. Culture isnt that important to the Vasari in general. but the damage boosts it provides can make the difference between victory and defeat in a close battle.
1. Make the tech mobile ruler ship give a boost to all your ships or your titan if you own no planets. Such as increased movement speed through real and phase space or a boost to the titans shields and hull.
2. Make the tech that gives the tax income from their caps give them double or triple income if they have no planets.
3. Make shipbord labs give them a reduced amount of labs for every planet they own. something like the min amount of labs being .25-.5 with the max being the 2 it is now.
4. Let us choose what comes out of the Phase stabilizer. In effect it would be like a frigate and capital factory combined into one. but the ships would be built instantly and more expensive.