I've considered hunting down an FDS in the past. Hardware reliability issues aside, I just can't justify it when I can't think of a game I'd really want other than Mario 2.
Yeah, it probably doesn't make a lot of sense outside of Japan.
In Japan, however, FDS is the only cheap way to play classics such as Metroid, Zelda I & II or Castlevania I & II.
Cartridge versions exist for some of those games, but they're rare and expensive.
On the other hand, disks are cheap, and Disk Systems themselves can be bought for a few hundred yens (less than USD10).
Of course, it's almost impossible to find one in working condition at those prices, but luckily, most suffer from the same problem: a broken drive belt. Replacing it gives them a second youth, and replacement belts can be had for about USD 1~ (or it's even possible to make your own with vinyl tape!).
I'm interested in tracking down an FDS, but I might hold out for a Sharp Twin Fami.
Twin Famicom has one big advantage nowadays: it has RCA outputs, so it's usable out of the box, while red-white Famicoms require modding to even work on modern displays.
They do suffer from the same drive failures as regular FDS, though, as the floppy drive inside is the same.