Make more of the same pokemon or save candy?
I have a 91% Mud Slap/Stone Edge Rhydon with 52 Candy. Maxed out to 2967 CP at my level (he's at lv 33.5 right now). Have another two 91% Rhyhorns lined up, but they're from eggs so only level 20. Should I make another Rhydon or save the candy to max my current one out further (though I don't really see the point as he is already mighty strong at 3k CP)?
Similarly I have two Arcanine at level 30 (one 89 IV one 51 IV). Both with Fire Fang/Flamethrower. I also have a Bite/Fireblast at level 20. 82 IV. Should I upgrade the bite/fireblast one or make another one from a 89% Growlithe?
Answers
Powering up your existing Rhydon is not going to get you much further. Might as well start working on another one. However, wait until you have enough candy to evolve a Rhyhorn and power it up a bit, then if you find a better Rhyhorn before you can use that one instead.
For Arcanine, are you wanting another gym defender, or an attacker? Bite+Fire Blast works pretty well for attacking. Bite does a little less damage than Fire Fang, but does charge energy a little faster. The most common grass pokemon you are likely to see is Exeggutor, which is still weak to both Fire Fang and Bite.
With a few very specific exceptions, I don't really plan on powering up most of mine much past level 30. It's just not worth it to me to spend so much more stardust and candy for only half the gain. So my advice is to leave your Rhydon where it is (a real beast) and work on another one. That's what I'm doing, actually. I took my MS/EQ to 30 (2774) and am saving candies for another evolution one day.
My advice on the Arcanine: some folks prefer Bite over FF because it's faster and builds energy quicker. So that's all down to personal preference. But I would argue to leave yours where they are. If you get lucky and catch a high CP, acceptable IV Growlithe, then go for it. That way, you won't be out any stardust and you might get lucky with, well, anything except Bulldoze. But I think your two at level 30 will more than serve your needs for fire mon in the meantime.
As everyone advices I also won't power up mons more than level 30 with a few exceptions, the ones I am going past 30 are Dragonite, Snorlax, Vaporeon and a 100%IV Gyarados and Blastoise.
Still waiting for that Lapras with good moveset, hope it is my Christmas present :D
NOTE: When you get to level 34+ the levels are too long to get that you will have enough dust to power the ones you left before ;)