I see absolutely no shelf life issue here. But with that said...
Here's a thought. Storage costs money. You need garage and shelves and boxes and marking of boxes and ladders to get to the boxes in the back, and remembering what you did buy (out of sight is out of mind.) Place a dollar value on the storage and compare that to the potential cost savings.
Additionally, what happens when that car get stolen or wrecked in an accident next month. You are now the proud owner of brake parts you can't use. Yes you could sell those on Craigslist or Ebay or wherever, but I'm guessing you will only be getting 50% of your original purchase price.
If you really believe the price of the parts will go up, then take your money and purchase some financial stock in automotive parts companies. (My vote here.) Online trading is very cheap. And if you really want to make that money move, I'd buy a call option spread. You can easily take $100 and move it to bigger numbers.
Cash is good. Storage is a hassle. There is risk to buying something with the intent of using it later (like the car is no longer there...)