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)
Founder of GMAT Club
Just starting out with GMAT? Start here... | Want to know your GMAT Score? Try GMAT Score Estimator
Need GMAT Book Recommendations? Best GMAT Books
Co-author of the GMAT Club tests
Have a blog? Feature it on GMAT Club!
GMAT Club Premium Membership - big benefits and savings