Probably depends on the R rating of the insulation already in place. At best, I'd level it out. Do you plan on running electrical or plumbing under the floor? Might be best to take it out if so. Of just take it all out, if the attic is over the house (you don't insulate between 1st and 2nd floors, so why between the attic and the level below?)

Don't forget to insulate the more important part, the ceiling!