this paper is a relatively thorough theoretical discussion of various aspects of a 3.2 ILS slope in Frankfurt:
https://www.ff.tu-berlin.de/fileadmi...g_Schubert.pdf
The theoretically predicted noise benefits due to a 3.2° glide slope angle were confirmed in the full flight simulator study. However, the benefits were slightly smaller than expected. Only direct noise measurements from real flight operation will provide the final proof.
the subsequent 2 year trial in Frankfurt
showed a clear reduction in the maximum sound level ranging between 0.5 and 1.5 dB (A) depending on the monitoring station and the aircraft type.
0.5 to 1.5 dB reduction isn't a whole lot, but it's more than what newer aircraft/engines have contributed for arrivals over the last decade, as a lot of the noise is from the airframe. Evidence also suggests the noise footprint area is reduced by about 5-10% for every 0.25 degree increase in glide slope (...and I can hear some people asking "so where will this end?", but due to aircraft certification limitations I think that's not a realistic debate now).