Agreed, it won't really sell for anymore because of the springs and the buyer will have a choice if you offer them off the car. If he/she is not interested you could always flog em after. Not only that, personally, if I was selling the car, I couldn't be bothered to rip off all the springs and stick lower ones on just because I've got them. Its up to you though. If you've got the time and actually want to do it, a 40mm drop is pretty much the norm and doesnt look slammed.