Allow me to share my story, if i may.
I had a 328xi coupe, and it was a lease. I put a shit load of mods into it, mostly cosmetic, because God knows you can't get a hell of a lot more horsepower out of an N52- I know, I've tried early on then gave up when reality hit.
At the end of the day, it still wasn't enough. I compare it to a super sweet girlfriend that was reliable, and always there for you but just didn't put out.
A lot of money went into her, and I fell in love again for a short time each time I put on this mod, or that mod, but at the end of the day, she doesn't didn't do it for me (especially after several 335 loaners- damn you BMW!)
I bit the bullet, traded in 3 months early, and traded up to a 2011 335 M-sport convertible, fully loaded to the teeth.
I couldn't be happier. I only wish I did it sooner instead of dumping shitloads of money into a car I knew wouldn't do it for me long term.
Thankfully, the majority of my mods were sold again, and I ended up making up a good part the money.
In my heart I knew all it all along, from the moment I drove off the lot with it, still eyeing that 335 M-sport in the corner that was JUST out of reach...if I had only had just a few more months on that lease of my 2006 325, who knows...
You already have your answer, you know what you need to do. Good luck.