as someone who was around when all of the coins mentioned in the OP were launched, i can tell you something about each of these coins that is probably not known by most of the current coin community:

Peercoin - legit, this is the only coin in your list that has technical merit and real benefit to users. the guy who made it, i can't remember his name, he also made Primecoin. His coins are novel, but show a devotion to creating useful features instead of creating coins to pump and dump. the idea of staking, such a lasting accomplishment. If i were investing in old coins, this would be one of them.

Feathercoin - started out as a pump and dump scjeme, which was very common back in those "wild west days" of crypto. i'm surprised to know this coin is still alive, probably kept alive by the bagholders in hope they will one day ROI. no one truly believes in this coin, and it is completely unremarkable in every regard. the algorithm used is not a feature, its just a novelty, like other countless alts.

Unobtanium - was made by an employee of the University of Idaho, i think he was an IT guy. He made the original guide for creating altcoins, his username is shakezula. He's a really good dude, but this coin was created for no real reason other than a chance for the dev to mine lots of coins and then sell them for profit. knowing him, he probably still actively trades the coin and supports it. IIRC, its feature was scarcity, an idea which was directly ripped off from the ancient coin that preceded it, called Bitbars. i understand if you support this coin. scarcity is perhaps a good feature,and perhaps it could lend in making the market stable, since the quantity is low and grows very slowly.

Terracoin - is also an altcoin, but it was not made with the intention of scamming. I've had some squabbles with the dev in the past, but overall he's a good person. The coin has questionable use, but the guy who made it didn't do any shady stuff, was never a scammer, was always saw as someone of high ethical standards, and last i checked he was quite active in keeping the market alive for the coin. if you want to support this coin, its cool, but its novel. it didn't add any new features.