Machamp

I think it is not a good use of dust and semi-rare candy. On the other hand, if it floats your boat, go for it.

Even with karate chop/cross chop, machamp is not a strong Pokémon worth powering up.

Sure, power it up. It's not often that one gets a 100% IV mon that has a high max CP and an A-rated moveset. Machamp might not be a great defender in general, but you will have the best defensive Machamp on the planet, and in doing so, you will add fun and diversity to the game.

I powered up a Cross Chop/Submission Machamp to 2500, and he's not a stunning defender, but definitely better than Gyarados.

I'm not swimming in Lapras and Snorlax, so have to use suboptimal defenders to supplement my best defensive Pokemons - If you've got enough Tier 1 defenders don't bother, but with his fairly high cp he's usable - I'd probably rate him around 2.5 on the tier list.

Machamp candy isn't really valuable (I wouldn't bother using one as an attacker - will just cope with a Snorlax of the same CP if you dodge charge moves).

I can gather dust any day, getting Snorlax/Lapras candy takes a lot of walking, so I don't mind spending dust on different options.

I would definitely power it up. You should be able to get it above 2500 CP, which would put it in my top 10 on CP (I'm level 32) and certainly would hold a decent position in many gyms. Maybe it won't be a Snorlax, but it will make a nice change for those attacking/prestiging against it, and adding diversity to gyms increases their overall strength. And lets face it, most gyms these days are full of useless Rhydons that I can kill in a few seconds with a decent Vaopreon: Your Machamp would at least make me think about what to reach for when attacking!

The moves are not too strong, but good max CP and no easily exploited double weaknesses like Gyarados or Rhydon and it is a fun mon to put in gyms,