Lovely looking car I have the same rusty brown interior in my E91 325i LCI.
Couple of things to keep an eye on:
If the Nox sensor is failing (very common fault), consider a Bimmerprofs emulator and removing the NOX catalyst, then you should liberate some more sound.
https://bimmerprofs.com
I have upgraded to a 330I manifold and map and am very happy with the results, this is effectively a factory upgrade as all the parts are identical so quite a nice boost and and takes the flatness of the car.
The biggest plus so far has been the map and new set of injectors, the injectors are a huge issue on these cars, interestingly the Inlet manifold with DISA valves only gives another 10-15hp, so it in the balance as to whether its worth it..
After reading lots and doing lots of diagnosis in Inpa, the easiest test is to let the car sit over night and then pull the spark plugs - if they are wet then the injector is shot, I noticed your exhaust was looking abit black - so worth checking... Also worth checking that you car is running in stratified mode in inpa, if there a problem it will be stuck in homogenous mode essentially a limp mode with a CEL light.
Did you keep the same hoses on the 340MM brembos? I have set just waiting for my disks to arrive..