It depends, if you sell it to a 50 year old guy, you might have to take it off but for younger person you can leave it on and try to get more money.
For trade ins, it got to be stock or they may not take it. You can to take it off and sell it seperatly but as I said, it depends on who the buyer is

 

I'm gonna try and sell it to a kid who needs a first car and has semi-rich parents. Because I really don't wanna have to go through the trouble of taking those damn springs off.

 

^what mods are you planning to take off any ways?
springs aren't such a hassle to take off IMO

 

well see I have this thing were I wing everything and had no idea what I was doing so me and my friend were like lets go for it. so all in all it took 6 hours. I'm just gonna leave on the springs and take off the intake and exhaust now. rest should be fine.