If you're doing this it wont hurt to get all new shocks but thats up to you. I did this about 2yrs ago but was too cheap to change the shocks as they looked to be in OK shape. I wouldn't say its required to change shocks from a lowering point of view in other words I don't think anyone makes special shocks for these lowered cars, only heavy duty type stuff.
Btw if your car has the self leveling system the rear shocks and springs are different. With the self leveling system supposedly you can adjust rear height, I havnt played with this though.
As for the spacers (rubber shims that sit on top of spring) they come in different thickness, you can put thicker in the rear and thin in the front. I dont know why these cars over time tend to be high in the front and low in the rear.
Over I'm happy with the stance of the car and relative handling though its still a BOAT.