Rare Candy

And your storage is maxed? I have to tell you, at that point you probably should be spending your rare candy on something since there are multiple great candidates in the game already. I was struggling with between 500-600 for the longest time but then they released the weather trio and I got a Mewtwo and now I've barely climbed back to 200.

I don't agree, I think it's a good thing that the limited storage incentivizes people to spend them instead of hoarding absurd amounts. There isn't really any good reason to hoard.

How about, I don't know, maybe converting it and using it to power up Legendaries? Or spending fewer coins on raid passes, which will only increase your obviously unnecessary candy stash, and using these coins to buy storage upgrades instead?

From a financial POV, clearly Niantic does not want players to accumulate large amounts of rare candies to max out future legendaries on their first day.

Pump 80 percent of them to your strongest legendaries or rare powerful pokemon

I keep 250 in my bags (out of 1500 bag space) should I ever find a legendary that I want to max out early on in that legendary's month/week/period. The rest are poured in legendaries that I want to power up at some point.

First world problems...

Your problem isn't a lack of storage, it's a lack of knowing where to use it. If you have that much candy saved then you're clearly neglecting it's purpose. Hoarding it serves no purpose beyond taking up storage. ...That alone should be telling you something. You obviously have no problem acquiring the candy, so why bother not using it? lol

You can convert them into regular candies without spending them (powering up) immediately. Do you have a Rayquaza, and do you ever plan to power up a Rayquaza? Go ahead and convert some candies, which can then be used on any Rayquaza any time in the future. Same with any other legendary. If you have a Mewtwo, that is a pretty safe bet. And if you really have a huge surplus and no foreseeable use for them, convert some into Feebas candy or Beldum candy or Bagon candy.

Convert them to specific Pokémon candy. You don’t have to spend them.

I was super happy to get even a 69 IV mewtwo just for the ability to finally be able to move 60 rare candy. I haven’t powered it...I just need a place for the rare candy.

I have 60+ in moltres, Entei and Suicune and Articuno...each... that I haven’t powered also. Maybe someday but for now, just somewhere valuable (20km per candy if you walk them) to get the rares out of my bag.

As you only power up 100%, including legendaries, there is only one solution - keep raiding until you catch another 100% legendary. You should be out there right now. Good luck.

Well, if you only power up 100 and do not want to convert them into any useful candy, you may as well transfer them and problem solved. Keep only 200 and power up the next 100 poke you get