I did this on my 330d five or six years ago now and replaced the original bushings with the same Powerflex ones you've fitted. I don't think I noticed any difference in ride quality, but cornering at higher speeds felt a bit more stable. I think I replaced mine at about 150k miles, the car is now on 207k miles and I haven't had any issues with them. Count yourself lucky as it looks like your brake lines have been replaced. I did those on mine this year and even though I cheated by not routing the new line over the fuel tank as per factory it isn't a job I want to repeat in a hurry - especially on the driveway. My suggestion would be to clean up the rusty bits on the underside, especially around the RTAB pockets, battery tray, jacking points and boot floor. That is if you plan on keeping the car for a while. It is a job I did at the same time as replacing the brake lines. I will have owned mine for ten years in January. It isn't worth much any more, but I still like driving it, even though I have an E92 335d as well.

Underside of that thing reminds me a bit of digging up ww2 stuff.

Should do the break pipes and splice in new union ends while your there. Cheap fix.

Did you notice a difference in ride quality compared to factory bushings because most people i know say that its really hard after replacing with poly bushings

How do you remove the whole trailing arm?

where abouts in the uk are you located? underside looks rusty