Unless your financial situation is incredibly secure, the correct answer is save/invest it. Just like you may unexpectedly receive a windfall, you never know when you will have an unexpected expense like a car repair bill.
But if you have to spend it now, a set of sticky tires will make the most difference in your daily driving experience for the money.
agree 100% with both points.
I will probably never do this, but right now, I'm thinking that after replacing tires (and/or wheels), an FMIC will be the next most-beneficial option. ...I live in a rather hot and humid place though, so it isn't the same benefit for all owners.