Machamp is the best fighting type available and will be for a long time. He's good to fight Blissey, Snorlax, Lapras and Tyranitar, that's why he's rates with 10. You can't have enough of those...I have 4 powered up myself after getting extremely lucky by catching a 96% lvl 25 and a 82% lvl 28 from a nest.
Still worth it to power up Machamp?
I only have one Machamp (96%) at level 30. I've been doing every Machamp raid I can and I got my next best Machamp today. It's 89% 14A/12D/14S and it came with C/DP. For perspective, this was my 6th successful capture from a raid, and I'm not counting on TMs anymore so the fact that this one comes with the ideal moves is a huge bonus. I don't have very much dust, but I don't have any hugely pressing needs. Is it worth powering up another Machamp at this stage in the game?
Answers
They're useful for Tyranitar raids which are in turn, useful for the upcoming Mewtwo raids.
If you've got enough Tyranitars or maybe your local area is populated enough to always have people at raids, then you don't really need a powered Machamp.
If less people are around so quality of Pokemon is important just to be able to finish a raid, then consider powering it up if you can't do Tyranitar raids consistently e.g only if it has Bite
Since you're only powering to 30 and not the next Counter breakpoint (lv 36 with 15 attack), having "only" 14 attack won't be an issue.
Raids where I'm at tend to be boom or bust affairs. I'm not opposed to powering up over 30, I just haven't had the need. It's nice to finally have a great Machamp, but it feels like a luxury to an extent. My thoughts are keeping it at 20 for now. I suspect that one legendaries have run their course and the best available options are the tier 4 raids I'll want to power him up. I kind of wanted to hear if others felt strongly one way or another.