Hey, I usually end up in the diner, cost be damned, if it's available. The only time I think I grouse at this point is either if I'm stuck on a Regional (actually mooted since the new Panache food service more than cuts it), locked out of the diner on a coach leg (it's happened to me once, on an overcrowded CZ at Christmastime), or otherwise end up in a crunch.
As to the food replenishment, with the cafe I'm actually wondering what the sell-by is on that stuff (i.e. if it couldn't make a round trip and simply be sold at the start of the new trip...not that I'm advocating selling stale food [that happens anyway],
As to the trackside stuff, the other option would be to subcontract. Generally with things like this, you've got DIY, you've got subcontracting, or you've got letting someone else handle it entirely. Because of pay grade issues and it being a distraction from their main business, Amtrak handling it is unattractive. Letting someone else handle it becomes an option, but there are obvious problems with that as you mentioned. That said, arranging backup deals in a few towns at the back end of the Builder's route might not be a bad move for when blizzards strike. That leaves subcontracting, where Amtrak pays a company to run the cafe but keeps any excess. If there were enough trains through ABQ, DEN, etc., then it could make sense to do this in a way that is accessible from both the tracks and the terminal proper. Note the bold, it's there for a reason...the assumption I'd operate under is that you'd post a small net loss from on-train traffic but you'd turn that into a net gain from the "other side" of the service (that is, in-station traffic).
The truth is that I don't think this would make a dent in the diner, but it would make a marginal dent in the cafe. If I'm Amtrak management, however, what I do if this works is I file this whole thing as being technically part of "food service" for the route(s) in question (including a footnote or two, of course) and keep the breakouts hazy (or just keep the books together and make them nearly impossible to disentangle without an expert team of auditors...even if you split the receipts by register, you can also divvy up the labor costs favorably, etc.)...and use that to say "Hey, look, we've improved cafe service!" Of course then I, the stats nerd, start bitching about accounting tricks...but such is life, and it's not like they haven't regularly altered their cost accounting for the MPRs, now, is it?