I think it was about a year ago when I did some math regarding buying points. As I recall (and my memory is getting shaky these days), only with the 30% bonus did it work out to 34.5 points per dollar. Presumably, when AGR 2.0 came about, the 'going rate' for using points was 34.5/dollar value, and Acela commanded 37 or 38 points/dollar. So, with the BEST of the bonus points deals, you're only 'breaking even' compared to using cash. Also, I've discovered that using points gets converted at higher-than-dollar-equivalent for the same train & accommodation. In other words, you will NOT be redeeming points at the 'saver' fare, but the 'value' fare, and possibly a higher bucket. My senior rate discount also disappears, too.
In effect, Amtrak has your money for what could be an extended amount of time without having to incur any expense or carriage. While the AGR 1.0 days had a better, and consistent buy points rate of 34.5/dollar, these days, unless you're getting that purchase rate, you end up paying a premium over what cash could buy. BUT...you do get a 5% point rebate when you use points. BUT...change your trip if you used points is automatically, unconditionally a 10% hit vs 0% cash penalty in many situations. As they used to say in Rome: "Caveat Emptor" (Let the buyer beware).
So now, if I'm going to buy points, it's strictly to 'top off' what's needed for a trip I want to book using points.
To all: If my math and/or memory is 'off' in the above discussion, please feel free to correct me.