Well, the Crystal Rings are by far the best armlet/ring/gauntlet type armor in the game, so if being as powerful as possible is your only concern when hunting items, you can't pass a couple of them up. Cursed Rings are the only way besides the Hero's Shield to absorb elemental damage, so they are useful in that regard. Many of the other drops are still the strongest weapons or armor of their type, or if outclassed by new Lunar Ruin gear, still have properties that make them very useful in certain battles or with certain setups.

And yeah, TAY is a nightmare for completionists. There are ten other tails besides the Pink Tails (Blue, Red, Green, White, Black, Ebony, Gold, Purple, Gray, and Rainbow), and all of them are much more annoying to get than the Pink Tail ever was. And don't even get me started on the Phase gear...

And the annoyance factor goes for the bestiary too. There's so, so, many missable entries, entries that require you to pull the Barnabas-Z trick to get (fighting an enemy your not suppose to kill to get their entry, saving on a separate file, then restarting the old file with that entry now on it), entries that are a pain to spawn (moon phases are the prime annoyance factor here), enemies that have up to five different variations (like Flamehound1, Flamehound2, Flamehound3, etc), and one entry in particular that requires you to replay almost the entire final dungeon (which is the longest in the entire series) AND beat one of the hardest battles in the game to get. If you're serious about 100% TAY bestiary, don't even attempt it without a guide by your side for that specific purpose.

Also, Interlude is notorious for having a ridiculously tricky bestiary to complete if you don't have a guide letting you know where and when and what to fight, since you're constantly going from one non-revisitable location to the next, and there are odd random encounters hidden all over the place.