Cutting costs has the potential to hurt ridership, unless it's done very carefully and in a very restrained fashion. On the other hand, they've probably tried to cut costs enough times in the past that I'd be surprised if there was much room to cut costs further without hurting ridership; they've probably already cut all the costs that are truly unnecessary costs.
And isn't improving customer service part of building ridership?
Beyond that, more/better rolling stock and improved track infrastructure is probably what will build ridership. That costs money.
That, and perhaps getting the frieght railroads to prioritize Amtrak better, which may not end up costing taxpayer money. On the other hand, it might decrease frieght capacity slightly, which might ultimately lead to the public paying a bit more for shipping and/or breathing slightly less clean air if it forces more stuff to go by truck.
That all depends on what kind of train you are on and what customer service is to you. On the Regional, operating the snack bar, answering the occasional passenger question, and trying to keep the train on time are enough to satisfy most people. Oh, and keeping the bathroom clean.
On an overnight trip, when I am paying for a sleeper, what will satisfy me is a whole different order of magnitude. I want a polite, friendly, and diligent sleeping car attendant who will turn down my bed at the appropriate time, and fix it up again the next morning, and wake me at a given time if I so request it done. And perhaps perform the odd service here or there in line with their duties. And I have had a few who have gone above that expectation, and I am more than satisfied, such that I tip more than my usual (overly-generous according to my dad) amount. I want a nice, tasty meal served to me properly in a clean, well presented environment. I want to be able to sit in the lounge with a nice drink and watch the scenes go by. I want everything to be acceptably clean. And I want the train to be nice. All of these things are not relevant on the short-distance Regionals. On the other hand, I don't care if the train is somewhat late. To a degree, if I am a first class passenger, I enjoy the extra time onboard.
So implementing SDS does not help customer service. Failing to repair or replace a disintegrating, rickety, and rattling 10-6 that smells distinctly like fecal matter on the inside, and kinda looks like it too does not bode well for my satisfaction, either. Serving a pizza that tastes kinda like urine is no help. It wouldn't stop me from riding the train. But it lowers my satisfaction. I have two choices for going long distances: I can drive, or I can take Amtrak. I am happier about it when I am satisfied.
Certainly satisfaction is conducive to increased ridership, but it isn't tantamount to it. The fact that gas costs people 3 times what it did before Katrina is a good starting point for what drives people to ride the rails.
The problem is that to an extent, goals 2 and 3 are contradictory. To replace or rebuild the particular 10-6 I am referring to that I rode in aboard the Broadway Limited god knows how long ago costs money. So does offering good dining service.
But anyway, I ramble too much.