The schools know that you are better off taking the GMAT while you are in undergrad (quite a few folks are doing it) and will ultimately discount the score somewhat if you apply 2-4 years from now. They will discount it for staleness and also for getting taken in undergrad (while you have plenty of time and a fresh mind - as compared to a 30 year old busy professional with family responsibilities)
So, I would say save the money and effort for now and perhaps take it later (unless you are heading for an MBA in the next 2 years)
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