5% @$250 =$5,000
So if I do the math correctly your purchasing a 5K bike and want to replace the wheels? I would doubt a bike of that caliber doesn't come with some really nice wheels.
If you race or other than yes it does make perfect sense to have a race set of wheels but otherwise I would not buy new wheels unless the wheel that come on the bike are trash.
What bike are you buying? What wheels does it come with stock?
I would probably drop the $250 on clothing or replacement parts if it were me with $250 in shop to spend.