In all my years, I can't tell you the number of racers who tell me that the reason they didn't win was because of their equipment.
Then, when you watch them race, they bang off of every board and can't find the apex of a corner if you point it out to them. It's so much easier to blame the equipment than it is to blame your own driving.
It is amazing how much speed you can gain from a car just by modifying the setup or your approach at driving. People tell me that they don't have a good enough battery or motor because someone pulls 5 feet on them down the straight, then I try to point out that they scrubbed off a ton of speed in the corner entering the straight and they don't believe me.
Very small adjustments on our cars can make HUGE differences in their handling. This can then translate into gains in speed. Spend your time learning your car and how each adjustment affects the car. That is the best tool you can have in your box.
But, at some level, money does come into play. And spending more can improve your speed, to a point. At the largest events, there are MANY drivers at each skill level. If you can get a small advantage over them, you can improve your finishing position by several spots. Unfortunately, it is not feasible to do this for normal club racing. That is why you see many drivers spending a lot of money on batteries and tires for national level events and then using that equipment for the rest of their club season.
So, spend money, but spend it wisely.