The AGR points and card aren't "worthless." Sure, it doesn't make sense if you don't intend to travel on Amtrak again, but I wouldn't expect an Amtrak-branded credit card to be particularly useful if you're not going to travel on Amtrak.
For Amtrak travel, the points are still generally worth around 2.89 cents/point, compared to full-fare value fares or sleeper fares, same as when AGR 2.0 started. It could be worth a bit less if you're able to use lower-priced ticketing options, or (potentially) if you travel during certain holidays when they double the points needed relative to cost (though I haven't seen that personally in a while.) But the points haven't been devalued relative to the cost of the trip (which is what I think of when I hear that points have been devalued.) Amtrak is simply charging a bit higher cash price, which raises the cost for points a bit as well. It's no different than how Southwest handles their rewards program.
There are still some redemption options available as well if you're wanting to simply get rid of it and cash out, especially if you're Select or higher with Amtrak. There's some
gift card options, or if you're Select or higher, points can be transferred to Choice or Hilton (up to 50,000 AGR points a year.) The value likely won't be quite as good as redeeming for Amtrak travel, but it's at least an option to get some value, thus making it not worthless.
As for me personally, I've generally shifted my spending away from Amtrak cards, simply because I've been taking less trips on Amtrak (mix of cost and travel time) and want to keep my earnings a bit more flexible. Right now I'm finishing up some annual spend on another card in order to get the value out of that card, then I intend to move my spend almost completely over to cash-back cards full-time (and cancel the card I'm currently using, as it has an annual fee that I don't get enough value from.) I keep the no-fee AGR card, as they sometimes have some good earning promotions (the 2,000 points for $1000 spend came at a good moment for me, as I had a couple of large transactions that I could use that card for) and it has the 5% redemption rebate for Amtrak travel. Other than that, I only use it for a recurring transaction each month to keep it active.