Any point to power up a dark tyranitar now?

It can be effective against Giratina, although there are better counters (Dragons, SB Mewtwo, etc.) If you don't need it for that, save the dust for something you need more.

I think you just wanted to tell us that you got a lucky 96% Tyranitar. Congratulations, nice pokemon.

Dark TTar is always going to be a good dark attacker. Sure darkrai and houndoom out DPS it but it can anchor a dark team pretty well against most mons which it counters. Also its lucky, so go ahead and power it up. At worst itll fade into a tier 2 counter to certain raids, which still isn't bad.

Dark Tyranitar is effective against the current legendary raid boss (Giratina), the current EX Raid boss (Deoxys) and four Gen IV legendaries (lake trio and Cresselia). The Lati twins, Mewtwo and even Lugia are likely to eventually return.

If you need him now, go for it. Ttar will also be a solid dark attacker. Since you got lucky, it is going to take less stardust to power up. The question is: are you trying to do small group raids? Are you usually raiding with a lot? If you have a limited supply of stardust and you aren't really using ttars then wait. If you want more dps and you don't have a full squad of ttar then power it up. Remember if you are in a small group and you overall you are one of the person's contributing a lot of damage in a raid then you get extra premier balls. At the end you have to decide if it's worth it with these questions in mind.

It's a lucky with great IV of one of the most meta relevant pokemon, useful for the current T5 boss as well as a lot of different T3 solos (Like Raichu, Alakazam, Gengar...). What are you waiting for? Even if Weavile comes out soon and out DPS Tyranitar it is still more glassy and has a different set of weaknesses due to Ice vs Rock typing, so having both will be great. In fact, dark Tyranitar is probably a better investment right now than a rock one.

Brag post.

Power it up - eventually. It's likely going to remain a great Dark Attacker for generations, so it won't be a waste of Stardust or Candies.

But unless you absolutely need it right now, I'd say wait until after Gen 4 is released and we see just how good (or how nerfed) other Dark attackers are before powering it up. It's likely that there will be other Dark Attackers that may be more useful to power up in the short term, so getting them up to Level 30+ might be a better way to spend the Stardust.

If you do need one right now, power it up!

There is, the only reason Tyrantiar's not the best giratina counter is the dragons out DPS it by so much, against the lake trio, cresselia and mewtwo and deoxys its still the best nonlegacy coutner.
Things that have competitive DPs like honchkrow and weavile have special evolution items required so that holds back their availability, and sneasel's also a rare species from what ive seen (yes its a raid boss, but so is the pre-evolved tyrantiar thats a tier 4 and gives 10 candy)

Maxed my second 98% double dark tyrantiar (this one lucky) yesterday because we get fog where I am and I plan on short manning cresselia and such without needing to spend tons and tons of healing items

I don't see a viable alternative to Tyranitar within the currently released mons. Taking into account that I do enjoy challenges like Alakazam solo, Gengar solo and duo, Mewtwo 4-men last month, etc, I have 0 regrets for maxing some out.