Gary,
There's nothing wrong with enjoying all the new boxcars that Lionel produced and continues to produce... whether they were 9200-, 9400-, 9700-series during the MPC/LTI years or WHATEVER new numbering scheme Lionel uses now in catalogs and on product box flaps.
But all those "other" boxcars are NOT automatic entries into the "6464 club" just because they are boxcars. 6464's were a special part of Lionel post-war to a lot of people. So for the most part, we're talking about the 30 or so boxcars that are pictured in Peter's snapshot posted earlier in this thread.
Did Lionel exploit the re-issues by attempting to extend 6464's into archive series, overstamp series, etc... among others? Absolutely. And many folks saw it for what it was and didn't jump on those cars the way they did Volume I through X three-packs.
If you don't buy the nostalgic element of 6464's, then another way to look at it is this... the 6464's became "collectible" BECAUSE there were a finite manageable number of them. It's not out of the question for serious enthusiasts to buy 30 boxcars. But when importers push that to another level -- for example, like Atlas-O did with 40' reefers -- then folks lose interest in trying to "collect" an entire series. It just gets too mind-boggling. And with most folks more interested in operating trains rather than just collecting them today, it doesn't take all that much for folks to lose interest.
Many of us thought Atlas-O's 40' reefers were gonna be the modern-day equivalent to Lionel's postwar 6464 boxcars. But Atlas-O ruined a good thing by overproducing them... and then they even came out with 36' reefers and overproduced that series too. As a result, folks pretty much bagged it after a few years and nowadays just yawn when Atlas-O announces yet another group of reefers.
So back to 6464's... best to just keep them defined as how most folks remember them. Younger hobbyists will have enough newer trains that represent a special time in their lives, but those items will likely not be 6464's.
David