It really depends on you.

How competitive are you and what are your priorities?

If you have the extra fundiage and it's not allocated to making you or your car safer, then yeah, go for it. If you're just starting out with the whole racing thing, spend your money on safety gear, or use it to get to the track.

Also, keep watching for folks selling off old stuff in the classified section... you never know you might find a deal.

It never hurts to have an extra set of wheels even if you eventually decide to put out the cash for the 13x6s.