What to do with Spare cash?

[Galaki]

UFO Afterlight (PC)
very steep learning curve if you're new but awesome tactical squad game. It's like a cross between turn base tactical and real time stragegy.
once you get into it, it will eat up many sleepless nights and many months.

you can customize your soldiers to be jack of all trades or master of 1, blah blah. Highly customizable troops.

the weapons you can also customize with add-on such as scope, stabalizers, etc...
you can have multiple types of ammo, too, on certain firearms

there is also research tree, something like civ.

there's production

there's base building/upgrading

aliens also invade you base, so you get base defense mission, too

There's also a bunch of mods, too.

They should have a demo that you can try, also.

Be warned. It probably has a higher learning curve than Civ.