Tourism is a small part of your income regardless of what you build. Why not add another aspect to the game. Vegas style!

Add a branch to the entertainment tech tree that allows you to build tourism related features, like casino's. Even build another type of starbase that depending on how many influence lines it intersects creates tourism cash. Then you build mods that increases the cash generated.

This allows you to generate income with the option of having lower taxs and you could create a super project that boosts this even further and so on.

Anyways this would allow you to tweek the income a little since right now if you play the way I do, its a war just to stay below 20k penalty on income. Yes you would have to defend these station, as they have to be totally unarmed, however nuetrel civilization would get a general benifit from all civs, while good and bad would get a much higher income but from those civs only, more good civs, more cash.....more bad civs more cash.

Anyways just thought this could be a cool addition to tweak things a bit.