I have both CDs. The 20th Anniversary Remaster seems to have a few extra tracks over the original 1989 release. That's why I bought it.
In any case, initial listening of the Remaster is favorable. I can also verify that the bass is enhanced and the music seems a few dB louder overall as well.
Remaster Album Gain = -4.06 dB
Remaster Album Peak = 1.028609
Here's a more complete analysis of some of the hit tracks, comparing both the original and the remaster. I will present Audacity graphs of the remastered tracks only.
NOTE: All tracks ripped by EAC and encoded to MP3 using LAME 3.98.2 -V2
High Plains Drifter
======================
Original ---- Track Gain +0.67 dB, Track Peak 0.778856
Remaster -- Track Gain -3.06 dB, Track Peak 1.028609
Audacity graph of remastered version

Hey Ladies
======================
Original ---- Track Gain -2.13 dB, Track Peak 0.995883
Remaster -- Track Gain -4.54 dB, Track Peak 1.015156
Audacity graph of remastered version

Looking Down the Barrel of a Gun
======================
Original ---- Track Gain -2.62 dB, Track Peak 0.956450
Remaster -- Track Gain -5.32 dB, Track Peak 1.020670
Audacity graph of remastered version

EDIT: Forgot to add the remaster album gain/peak.