While mine has quite a few mods done, even some very extensive or next-to-impossible ones, I'd like to mention 3 or 4 of them that I use basically all the time...

-The steering wheel. It is an M-sport type, I later added shift paddles and heating. It is an awesome add on for winter - I use heating literally all the time.
-Ventilated seats. A great feature when the car is parked outside on the sun, no more sweaty back. Also more comfortable than sport seats (that's why they're called comfort seats, right?).
-X-delete. An E60's x-drive makes it pretty understeered, so for winter I have it set at 50-70% (still a bit understeered unles you're playing rough with it) and in summer I set it at 5-15% so it is basically a RWD car, but with much more control when having fun.

oh, and a bonus one - dynamic headlights - it's a massive improvement over (stock) xenons. I mean - a really good feature, worth the hassle and expense of retrofitting.

Other than that? Reverse camera, sport mode, USB, ACC stop&go, a DSP 4-channel amp + a monoblock an a 12" subwoofer, auto headlight control (low/high beam), hybrid turbo and larger intercooler for good100hp gain, tuned transmission, tow bar to transport my motorcycle, lowered suspension... ...yes they are worth the money, but I could easily live without them.

 

So how much would you say you've spent on mods? Surely beyond the present book value of the car?