Power up Kyogre and Groudon?

I'd say if you have good (i'd say even a 10/10/10 would be worth it, preformance difference of a 10/10/10 from level 25 to 30 and a 15/15/15 level 20 to level 30 arent that huge, if it was maxed out, i'd say always go higher IV's, but for a boost that small comparatively, saved dust/candy is more worth it) Iv boosted ones, leveling up one of each wont be a big loss if its to level 30, as they currently are level 25.

Kyogre seems the more relevant of the two to have, given its effectiveness against Rhydon raid, and if we get raid days of the beasts, will be great against Entei. I'd recommend powering kyogre up as its great against groudon right now unless you already have high level HC feraligatr
Groudon on the other hand, as I have recently discovered isnt as good legendary, and even tier 1-4 wise (unless facing electric type tier 3s), against dialga, it lags hard compared to machamp unless weatherboost. One level 30 will be more than sufficient I would think.

Their exclusive moves likely wont be out for a while, given niantics shall we say slow releasing of moves and event pokemon. For reference, we dont have Psystrike mewtwo, a gen 1 pokemon, and the weather trio are gen 3, we likely wont get them until after mewtwo, which could be a very long time.

It will be out in the future?

We know it's in the game master. We don't know when or even if it will be out. They're still stupid powerful without their exclusive moves so if you do power them up it's not a complete loss. If Breloom taught us anything there's too much FOMO in the game to really get hung up on it.

Either way, not powering something up until you need it is a good rule to follow. There isn't a real need for either of them unless you need Kyogre to beat Groudon more reliably. Wait until the end of the event, see what comes out next, and decide then if you need either one.

I've gotten reasonable use out of my two maxed kyogre, but in general they seem unnecessary given that a lot of their uses collide with machamp who has other reasons to be maxed. I'd still recommend powering at least 1 since it is the best of typeb and actually matches or occasionally beats machamp in those cases.

Groudon likewise, is often overshadowed by machamp for example. Still as best of type it's probably worth pursuing one.

I'd recommend doing a lot to save on rare candy, and have trade candidates to try to get a lucky.

At this point? I don't recommend powering up ANY Pokémon unless you've got a specific use in mind for it. Niantic is tossing out way too many Special Event moves (Raid Day, Community Day, Breloom Event, Special Research Snorlax, etc.) to justify powering up any Pokémon without a goal in mind for that Pokémon.

But if you do decide to power one up, I'd go with Kyogre. Right now Water seems to have more versatility when it comes to just about everything when compared to Ground. (Though if you have CTM's to burn, Groudon with Solar Beam can be a BEAST.)

First rule of Pokémon Go is NEVER power anything up to you NEED it

Second rule of Pokémon Go is NEVER power anything up to you NEED it

Only possible exemptions are childhood and or personal favorites and the childhood and or personal favorites of friends family or significant others strictly for the purpose of annoying friends family or significant others

Boring... yes
Not a lot of fun... yes

But if you want to short man, speed raid, get those extra damage balls... it’s the price you must pay... the single biggest thing nobody talks about is that Pokémon Go is basically a time and resource management game so there is no point in powering things up you don’t immediately need and waste resources

I have a 100 iv of each maxed out and would say YES to level 30 is a great investment and anymore worth it too.

I had two Kyogre at 40 already and boosted one more to the last Groudon breakpoint (given that most of my raids during the Hoenn event would be Groudon). However, I would advise against boosting one as there are no legendary raids after the event that'd require either of the two. Keep the candy for after they have received their exclusive moves.