Save for Rhyperior or move on?

Ya sucks! lol But i would save him if you have room Gen 4 might not be for a long time, and I would not invest in him until then. Im sure you will have enough candies by then and maybe another rhydorn might be worth in evloving by then. Nothing like your 1st 100% IV I got lucky and got Gyarados for my 1st and only with bite and hydropump I jacked that bad boy up! lol

Save it for now. We are not yet sure how the gym shake up will effect the CP value and frankly Rhydon isn't that great except for CP imo. He could wind up with the best moveset after the mega evolution but if he doesn't it will not have cost you anything.

Wait till the gym rework happens. If CP is still king after that and you need a high CP rhydon in gym to collect coins, then power it up. otherwise don't invest in it and wait till gen 4. Even if you decide to power it up, wait till you have enough candies to power up to a CP high enough for local gyms. who knows, we might have a half-candy power up promotion during Easter as some rumors suggest.

Rhydon is a terrible defender with double easy weaknesses and also not a useful attacker in the current meta (I don't remember the last time I used my Rhydon for attacking).

The only thing that counts is CP, because of the current gym system, so you got the best of it with a 100% IV.

BUT... there's a gym rework coming soon... I would recomend you to save this mon as a trophy and wait for the gym rework to see if it's still worth powering him up.

I'm truly sorry for your loss, even if it's not a complete loss, letme explain: Rhydon is not really an elite attacker, Golem is a better Rock type attacker because of rock throw, and there's not much you want to attack with a ground attacker anyway. Rhydon is however an ok attacker into snorlax because he resists normal attacks (even if Snorlax's best defensive moveset is not normal type), and rock smash is not really worse against normal type pokemon... megahorn is awful thou..

I'd keep him but wouldn't power him up, unless you are in dire need of "defenders". What I mean by defenders is high CP pokemon that can sit higher than a blissey or a snorlax (sometimes). Maybe you'll have better luck with Rhyperior

Sorry friend. I got a 100% dragonite with Steel Wing/Hyper Beam. I feel your pain.

Save him for Rhyperior. IMO, other than its CP for gym placement (which could be changing with the revamp), Rhydon is a terrible Pokemon on both offense (awful quick moves and single-bar charge moves) and defense (crippling vulnerabilities against the meta's most ubiquitous hitter). You won't really miss not powering him up. I have a 3,100+ example, and I never use him for anything.

Don't spend dust and candies on him. Save him though.

At some point they may also allow us to reroll moves. Maybe at the cost of candies. 100% is great to have but that moveset is bad, really bad.

Unfortunately you can save your dust and what ever candies you have.