If that was mine I'd pretty much leave as-is. However I'd be tempted to do the following if I had the cash :
Aero skirts, as said above - even tough the car is black they look great. I helped srhutch fit his and was filled with envy. Also, they will eventually stop making them... But there will always be a market for them if you want to sell them on. About a £500 mod once painted.
Gaptech - about £100, unnecessary really but I like not holding the button for the roof and being able to open / close it from outside with little hassle. There is also always a market for these if you decide to sell the car.
Intravee - second hand the kit will cost you about £160, not strictly necessary as you have the aux input, but the Intravee also provides the ability to programme things like lock doors when you pull off, angels as DRL, one touch indicator flash when overtaking etc. Second hand market for this too.
Spoiler - a very marmite mod with regards to opinion on here, but I like it. Would probably cost you about £300 once painted. Irreversable mod though due to the adhesive used to stick it on - unless you can find a boot lid to swap on, or are willing to have the whole boot lid re-sprayed.
Wheels - personally I'd stick with stock, but that's just me.
I don't know the details, but I have read that cruise on the ///M is a complicated retrofit that some will tell you cannot be done. I don't know why they say this though.
My advice - take your time and enjoy the car, it is an almost perfect specimen
