Ok, I went with the last iteration since getting proper inflation data for this year is nigh-on impossible. 2013 can, however, be found and so I have used last August's numbers per that thread I keep updating once or twice per year:
Jul 1971, WAS-NYP
Coach: $13.00
Parlor Car: $23.40 plus $3.15
Metroliner Coach: $17.00
Metroclub: $27.40 (plus $3.15?)
Jul 1971, WAS-NYP (adjusted for inflation via CPI)
Coach: $74.80
Parlor Car: $135.00 plus $18.10
Metroliner Coach: $97.80
Metroclub: $158.00 plus $18.10
Jul 1971, WAS-NYP (adjusted for inflation via per capita GDP)
Coach: $123.00
Parlor Car: $221.00 plus $29.70
Metroliner Coach: $161.00
Metroclub: $259.00 plus $29.70
Aug 2013, WAS-NYP
WAS-NYP (Regional)
Bucket E: $49
Bucket 1: $84
Bucket 2: $120
Bucket 3: $145
Bucket 4: $164
Business Class: $41 additional
WAS-NYP (Acela)
Bucket 1: $152
Bucket 2: $180
Bucket 3: $205
Bucket 4: $231
Bucket 5: $259
First Class: $116 additional
I put both sets of numbers up for information, but the bottom line to be had is that the difference (at least on NEC-South) between the regular trains and the Metroliners was a lot less than the difference now between the Regionals and the Acela while the apparent price difference for coach vs BC/Acela BC vs Acela FC is a lot bigger. I broke the "plus" out for the accommodation charge because I wasn't sure if those accommodation charges were rolled into the higher fares for the regular trains (I don't think so) or the Metroliners (I have no idea).
Going with per capita GDP as the measure, the 1971 fares are middle-bucket for Regional coach, high bucket and then some for Regional BC, low bucket for Acela BC and high bucket for Acela FC.