The OP doesn't seem to be on a tight budget having already spent 1,000 Euros on parts.
The main focus seems to be to lighten the total weight of the B'ton. Lighter parts make
carrying the bike easier. But in regards to parts that are spinning; you can also go fast(er)
by decreasing rotational mass. It may not matter on a 1 mile ride to the train station; but
on long and/or hilly rides - it might be worth it to some folks. I ride my Brompton on a lot
of charity rides; Tour de Cure, NY Bike MS, NYC Century. Some of these rides are quite hilly
and some are over 100 miles/160 kms. Swapping to lighter parts have helped me on these
trips. Schwalbe Kojaks(folding), sometimes Primo Comets, ti pedals, Ultegra chain, etc.
Here I'm passing a bunch of folks on a slight uphill on the Brooklyn Queens Express:
https://www.youtube.com/watch?v=lmFU...6zPoymgKaIoDLA
Here I'm passing a few roadies on a steep section of Walnut st.:
https://www.youtube.com/watch?v=ROYH...6zPoymgKaIoDLA