Should I power up my Rhydon

The RS/SE is okay for a blissey and snorlax. It is a tank, but you have to put up with how painfully slow it is (Rhydon's attack stat isn't bad but these moves are so slow). I have one at level 30 but only because I caught it at 24xx cp to begin with so I only had to power it up 3 levels.

If yours is not at a high level (at least 25 in my opinion) then I wouldn't recommend powering this up.

I do imagine that they will rework to make some non-stab moves to be competitive in some way rather than be strictly inferior, but the STAB moves should be the better ones overall in any case.

I'd do the he greater iv option, if any. Rhydon evolves into Rhypherior in gen4, giving it a potentially good moveset

If you can use it TODAY in a gym and get coins/dust, I'd power it up...I've maxed out all my defenders and keep maxing them even with the gym rework...

The reason being is candy/dust is constantly flowing into your Inv...Pokecoins cannot be gotten any other way for free players (ME) so those are worth a lot more than candies, dust...

I've already maxed both inventories and sitting on over 6k in coins all from gyms.

I also think ANY gym rework will make Pokecoins harder to get so yes, there will be a gym rework, it will probably make coins a lot harder to get simply because more people will play and knock out your gyms if it's half fun to battle...(remember, gyms are all easy, just boring and time wasting for a lot of people...).

Even with that, I have near 1 mil dust again (gyms probably help a lot actually) and I don't power up many attackers.

Gym rework could also be delayed so 2 more months of coins can be worth a lot if you aren't spending real money.

Rhyperior in gen 4 is also nice insurance so even with crap moves now, you can evolve when gen 4 hits and may get something useful.