Cuban,
Yes, the downwash does give the aircraft lift however too much whilst the aircraft is travelling forward at 500+ mph isn't particularly good.
Draw a picture...The effective angle of attack (AoA) increases with downwash meaning that the lift is not perpendicular to the direction of flight but is actually pushing the aircraft upward and backward. (I only wrote that because it says on your profile that you're a student so you'll know what i'm going on about)
Also, winglets reduce the effect wingtip vortices have if nothing else but again this would be mainly at low speeds where the induced drag is at iits greatest.