Definitely add it, and I would go for it in carbon fibre.
When I ordered my M3, I also bought the front splitters and rear spoiler (carbon), was so unsure about it on a white car. So pre-pdi I popped over and saw them offered up to the car in the work shop. Took all of about 1 second to realise it was definitely the right move.
So you could do the same, ask to see it offered up before making a decision.
If you plan on doing this yourself, I'd recommend gluing it on - not using the tape. A glue called Betalink is what BMW use.
F10 M5 Competition White / Sakhir Orange
Loaded, Akra carbon titanium exhaust, Carbon trim, Carbon spoiler, RKP carbon front lip + diffusor.
F31 330d M Sport (Alpine White / Red)
Loaded, 405M 20", M perf: skirts, brakes red.