Machamp Investment

I have never found a need to power mine up...but if you want to, thengo for it.

Depends. If machop are common on your town then wait for a better one, if you're lucky you can catch one at higher level too. But if you don't care about IV, machop are rare on your town and you don't have other machamp in your team, then go for it.
Futhermore you can wait for a return of Machamp in raids too.

Note that it has a double legacy moveset, but Stone Edge isn't that good. Karate Chop is about even with Counter because of higher energy gain in PvE, but lags well behind Counter in PvP.

If you're looking for a good one for PvP, and this one has low attack, it could play well in the Ultra League with TMs, assuming you don't mind wiping out the legacy moves.

But I'd argue your best bet is to wait until Machamp comes back to raids, and try to catch a weather buffed one. That would start you off around CP 2100, and give you a fair shot at the best moveset, Counter and Dynamic Punch.

Now, if the CP were lower, and it has Cross Chop, that would play great in the Great League, .... Alas.

for gyms and raid, you would prefer Counter - DP

KC and SE are both legacy, I would keep it as a trophy

If you want to power it up, I would unlock DP as second charged move: Karate Chop isn't Counter, but it's kinda nice too.

I see you're low on candies:
Do you have at least one already powered-up Machamp?
If you haven't one, I would prioritize this and power up the highest lvl with good IVs, before powering up this low-lvl 60ish%

IMHO Machamp is more a PvE than a PvP mon

I wouldn't. Machamp is more of a PvE pokemon and C/DP is the best moveset for that. Also the currently available Rock Slide is better than the legacy Stone Edge.

Keep it as a trophy. Who knows, they might buff KC or SE for PvP in the future making it more valuable.

I generally find no reason to power up a mon just because it has a legacy moveset unless I need it for some challenge (i.e. SC Gengar or Smack Down TTar). Furthermore, I'm reluctant to max out a 60ish% IV mon. Last, but not least, even if you found a niche for a fast Fighting and charged Rock move on Machamp, you would be better off with Counter / Rock Slide.

So if it was me, it would be a total NOPE and I would anyway keep it favourited as a collector's price. However, if you really like it, then it's all yours to decide what to do with your resources.

I wouldn't power it up but I'd keep it for novelty.