This is how the finish will be for the foreseeable future on the 21 inch plastic passenger cars.
In that case, they (Lionel) can keep them, or at least those models that are supposed to replicate polished metal finishes. That does not include the UP Excursion cars, which are much more accurate in the dome department than anything else produced to date.
Ultimately, it's a matter of personal preference whether you want a shiny metal finish or a poor paint substitute. Speaking purely for myself, I think that whatever paint Lionel's suppliers are using is poor. If you prefer something that looks weathered that's OK by me but I don't see many people wanting simulated dust, grime and corrosion on streamliner cars.
I also don't see either of the main manufacturers producing aluminum body cars ever again; GGD is now the only supplier of 3rail O gauge metal passenger cars but they also use paint for metal. The difference between that and polished aluminum is vast. Case in point is the Texas Special 21" aluminum cars produced by Lionel some 12 years ago, which as far as I am concerned capture the original look of the prototypes. This is the Stephen F. Austin observation car from that set and the only color photo of the prototype I have tracked down:
The third photo is a direct comparison of the aluminum body car with polished fluted panels and the ABS plastic version issued by Lionel in the first run of the ABS plastic cars. Actually, in person there's no comparison as the metal car wins the beauty contest hands down, IMHO.
A few years ago, GGD produced this fine model of the Santa Fe Great Dome car. The finish simply doesn't approximate polished metal but the other details and workmanship make up for that:
The bottom photo is with flash, the top without. This illustrates part of the difficulty of making comparisons based on photos posted on a webpage - they won't capture with complete accuracy what a finish really looks like or color differences. Actually, the finish on the Silver Meteor cars is better despite what the photos show as a close similarity.
FWIW I agree with the OP's reaction to the cars he got. No amount of saying that they look like a car that has seen a certain amount of service really makes up for that. But like I said, it's basically a matter of personal preference.