"my car"

I drive a 1994 Mustang GT 5.0 5-speed, and I LOVE IT!!!
However...It is 11 yrs. Old & things have well, lets just say, starting to go wrong.
My windows do not roll down on both sides (haven't in about 2 yrs) They want $300.00 a piece to fix them. I have gotten several quotes and it is always the same answer $300.00 a window.
I need 4 new tires (the 5th set) they cost about $750.00 for 4 new ones (that is middle of the road tires)
My tags and inspection are out!! Tags $70.00, Inspection $40.00
Oil is overdue $30.00
Total about 1,500.00

So...My ???? Is this: Do I fix these little minor things?? Or Do I take the $1,500.00 and put it down on a new "2005 Mustang GT convertible"???

I'm getting some money back from my Income Tax, and after I give my sister back the money I owe her, I will have some left.
I really want a new car, but I will not trade mine in. I would just put that one up in the garage and make it into my project car. We "sally & I" have been through way too much together.
I can not get this "new car fever" out of my mind!!!!
What am I going to do??????