After redeeming your points, then the points would be removed from your profile. For example you have 23k Xper, and you buy an Amazon Gift Card... then you'll go back to 18k, and lose Guru status as well.
Personally i'd still do it, although i wouldn't like it that much... but if i had to choose between top rankings and Amazon Gift Cards... well i'd go with the AGC
It doesn't work like that. GAG keeps track of the total points earned and redeemed. So even though the points come out of your redeemed points, you still have the full amount you earned counted toward your status.