CAUTION: The following post (or a page linked to) includes or discusses loading data not covered by currently published sources of tested data for this cartridge (QuickLOAD or Gordon's Reloading Tool data is not professionally tested). USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.
If the can is new and sealed, I would think the collector's market is a good idea.
In the name of full disclosure, I have a can like that of Unique I just found at my dad's house, looking in similar condition on the outside, but it was not unopened. It had been partially used and then apparently misplaced on the back of a shelf and replaced with a new jar of Unique. The old powder looks and smells fine. No red fumes, no rust eating through the can. If I pour a little out on a white sheet of paper and shake it a little and slowly pour the powder back into the can, there is no red dust left behind. So no classic breakdown symptoms. But Unique has a couple of qualities I'm aware of that may not be applicable to 2400. Alliant has a 110-year-old sample of Unique from the first lot that they keep underwater. Periodically, they dry some out and test it, and so far, it is still good. Unique may be unique in this regard. I don't know. Also, Unique is a fast powder. Slow powders have deterrents that can break down ahead of the rest of the powder, speeding up the burn rate. With the Unique, I can try a small sample at a fast powder load level (three grains in a 45 Auto with a 185-grain lead bullet) and see if it fails to cycle one of my 1911s. I expect it will, and then I can work up to a normal load, comparing it to the velocity I get from the same load using a new(ish) can of Unique.
Looking at my 1967 Lyman databook for the same or close-to-same bullet weights, all my old book data has slightly lower charges than the current Alliant data. The Alliant data is pressure-tested, but a lot of old loads were developed by pressure signs using components that have changed or are no longer made. Also, they used production guns rather than the tight-chamber SAAMI test barrels, so you'd expect they would tend to overcharge rather than undercharge. So, taken together, those lower old data load levels may mean the old 2400 was faster, or it may just mean the cases in use at the time were thicker and had less space in them.
In your shoes, if I wanted to use the powder, I would first make the same deterioration checks I described above. Ideally, I would have some modern 2400 I could use to compare velocities with very reduced loads first. Even better would be to have a barrel I could mount a strain gauge to for my Pressure Trace instrument and try to see what pressure the test loads gave me from reduced loads of both lots of powder, but that's not an inexpensive option.