I guess it would still be worthwhile monetarily but I would still be reluctant to buy a copy for that much, unless I was just planning to flip it as is. It's getting harder to find spare discs unless you're willing to wait a long time for one to show up. Game prices could still change and copies might go down if this game manages to get a re-release, if you're stuck with a copy missing a disc you could lose money on it.
Even for DS systems I don't bother picking them up if they're missing the adapter or stylus unless they're cheap(like $5-$10), it's a pain to find the adapters and it's getting harder to find a replacement stylus. If you have an original DS, good luck finding a stylus for cheap. I still need an orignal stylus for a system I have, they're not being sold new in stores and used game stores usually don't seem to have any available.
I have a copy of Final Fantasy VII missing the first disc, I haven't found a spare disc locally yet and I've got this months ago. I'm not going to spend much on it as I've found complete copies for cheap in the past. I got this copy for free along with other PS1 games.