It looks like a new...well, I can't call it a sale since it has an end date in 2025, but the bottom fell out on Acela fares. I'm showing $65 WAS-NYP with an RPA membership/$72 without one (add a few bucks to get full flex). NYP-BOS is showing up at $54 with RPA/$59 without (again, add a few bucks to get flexibility). And this is on almost every train starting 3-4 days out (there are some peak-hour exceptions, but that's about it). On quite a few days, this is undercutting Regional fares by a wide margin (I'll see a $65 Acela next to $150 for Regional BC).
If you've got an Acela ticket booked that's not one of those non-changeable fares, you'll probably want to look at rebooking. And if you've got a Regional ticket, switching is seriously worth considering. As an example, I had a one-way WAS-NYP that I'd booked a few days back at $170 (which didn't seem like a horrid deal - it was still cheaper than the neighboring Regionals' BC). I rebooked it for $70-and-change each way (RPA membership, flexible fare so I can upgrade at 48 hours out), so the round-trip landed like $30 below the original one-way.
If you've got an Acela ticket booked that's not one of those non-changeable fares, you'll probably want to look at rebooking. And if you've got a Regional ticket, switching is seriously worth considering. As an example, I had a one-way WAS-NYP that I'd booked a few days back at $170 (which didn't seem like a horrid deal - it was still cheaper than the neighboring Regionals' BC). I rebooked it for $70-and-change each way (RPA membership, flexible fare so I can upgrade at 48 hours out), so the round-trip landed like $30 below the original one-way.