Currently you earn rewards for racing and you get them if you pay for subscriptions or "top-up" using actual cash.
I've been really careful with my "in-game" cash and I've got quite a bit to spare at the minute, but I literally can't spend it on anything.
It would be great if I could increase morale on the team/of the staff, i.e. send them all on a team building exercise. Increase my drivers health back to 100% by sending them on a weekend of physical therapy. Pay to assist in the development of one of my "partrners" and therefore increase the effective of whatever they offer, e.g. help the engine supplier and get an extra amount out of the "performance". I'm sure there's many more others can think of.
I've got about 17 races before I reach level 8 and can buy the test rig and wind tunnel and when that happens I won't even use half the cash I've got. By that point I reckon I'll have earnt about enough to pay for them again! Daft that I've got this money, but can't use it.