I don't get you on that point. Sure it would be much more expensive than back in the days to start all over with the Neo. But isn't the hunt itself what we are striving for as a collector? And couldn't you enjoy the games even today from a player's point of view? I can affirm both questions although I have to admit the Neo has a bit 'worn off' after all those years. But still the games are great and a lot of fun.
Well, I thought a lot about your argument, the everlasting thrill'o the hunt, hence my late reply. Though I can only speak for myself, these are the three points responsible for the fading of fun to collect Neo Geo home carts...
ROMs -- If I can't connect collecting with playing, there's no fun to begin with and back then buying preceded playing, while playing a newly purchased game was
the thrill and the best way to enjoy it, too. There were no everdrives, alternatively only a strictly PC based, flawed emulation or ports, which were just ports. Now, with the NeoSD and comfortable digital re-releases, you don't need originals to play, thus the playing aspect is absent and you're just left with bare-bone collecting.
Prices -- I never was the miser type in regards to my hobby, but c'mon... is it really fun to spent an average of 2k on a game? This supreme price level was reserved for an elite, like the English Metal Slug home cart, now it's considered a bargain price for almost any post 95 title.
Bootlegs -- Conversions were also reserved for an elite like the English Metal Slug home cart, and easy to spot, too. Now, with this annoying flood of perfect indie bootlegs for even common titles the fun found it's final grave.
But that just me, the next gen of collectors, which doesn't know past times, can call the present day fun and turn my points of criticism into their own reasons why they have fun collecting Neo Geo originals to begin with. Just like I have fun posting on NG.com, while most old tymers hardly see any reason to feed what's nowadays the shadow of a shadow to them.