Time to spend my stardust?

Gengar SB = Sludge/Shadow Bomb/Ball? If it is Shadow Ball, power it up.

Poliwrath Water Gun? Is this a future obtainable moveset, you earned it by having a time travel? Bubble and Dynamic Punch is good against Houndoor, which isn't a raid boss currently.

Hyper Beam Dragonite? Don't power it up.

Rhydon with that moveset? Yes, a beast against Jolteons and Electrabuzzes.

Vaporeon? Yes, it is a beast against many famous tier 4 raid bosses, despite Hydro Pump offering more DPS, it is less risky.

Flareon and Typhlosion? They worths, but only when they have Overheat.

Cloyster? Dragonite isn't a raid boss, but it is common in most gyms.

Golem? Yes, good against Charizards for now and the legendary 3 birds in the future.

Exeggutor? If you really lack of Vaporeons, and need to obtain more from raids. By the way, it could be used against Rhydons (not the Megahorn ones) as a powerful backup.

Scizor is good against Exeggutors.

Gyarados: Don't power up, just use it at this level.
Rhydon: If this is your best double ground Rhydon, just use it.
Vaporeon: Don't power up, just use it.
Dragonite: Use a charge TM first.
Flareon: Ignore this, just evolve a new one. This moveset was once the best, but is now the worst non-legacy.
Typhlosion: Ignore this.
Cloyster: Don't power up, just use it. If you have access to the sea, go and get a FB/Av one.
Golem: Sure, power this one up.
Gengar: Don't power up.
Poliwrath: Don't power up.
Exeggutor: Don't power up, if you already have high level SoB Exeggutors (even if the quick move is psychic).
Scizor: If this is your only one with double bug, sure.

OP how much dust do you have?

You have any favorite legendaries? Recommend saving your resources to power one up when you get your hands on one. They are just around he corner for level 5 Raids. I would wait it out.