Being a post ban, I can't see it hurting the value at all. You can buy Colt uppers to keep it all Colt but expect to pay $150 extra for the little C mark before the forge mark.
Leave the front sight post as is, get a flip up rear sight, good one piece extended mount and any scope you'd put on a wood sport rifle for it's intended purpose.
Skip the carry handle scope mount unless you like to shoot with a chin weld instead of a cheek weld. They place the scope way too high.