Should I power up these pokemon?

All these PKM are worth powering up in my oppinion. Just ask yourself, which of them you need most and power this pkm first.
Vaporeon with this moveset is a good defender, the others are good attackers.

Hatched PKM IVs range from 66 to 100%, 77% fits perfectly. The Vaporeons who will be crushed by this Venusaur will not have the time to ask him for it's IVs.

I would power up none of them.
Vapo quite low cp and only usefull for def it s bettere to look for some low IV high cp Eevee to evolve.
Arcanine quite good but he got nerfed and way too low, you could power him for training around 1k CP depending on cp level in your area, 1k if you usually see 2k mons in gyms.
Gyarados super low, to be quite good he needs to be over 2.3k and not the best att set, use him to train against psy mons.
Venusaur sub optimal att set nearly 100 candy to max him for 30 and after nerf he wouldn't be that strong.
But definitely I wouldn't transfer them just use without power ups.
Maybe some day after a new stat changes of when you have much dust/candy to use consider them to power up

Food for thought:

I stopped powering up my 54% Vap (WaterGun/HydroPump) a few weeks ago because it has always done well and continues to do very well on attack.
Keep in mind it has 15 attack but the dust would seem wasted in my opinion as it's fine as it is.
If you're wondering why I powered up a 54% Vap it's because it's one of the first evolved Pokemon I ever caught in the wild in August and I didn't know about IVs back then.
But like I said, that Vap of mine has done well and still does when taking down gyms.
Pre-CP Buff I had it to 2103CP, it's like 2300+ after the buff and I've left it alone.
My stardust has gone up since saving on power ups like this. Same with some of my other Pokemon. I stopped powering them up. My Gyrados was 2000+ pre-buff and went to 2500+ after. I still haven't bothered powering it up as it's easy to beat as a defender and it's fine as is for attacking.

Save your dust for special power ups is my advice.
Also, I have some 100% Pokemon with 2nd tier movesets that I decided to not bother powering up.
So keep that in mind.

Annnnnnnd, some Pokemon don't need powering up to be effective on attack and for training.

For example, pre-buff Jolteon was fine for type attacking (water). I left mine at 1400 or something.

Stardust is precious. I know it's enticing to power up but make those decisions wisely.

I lived from power up to power up before the 2x xp 2x dust event recently. I'd power up lots of stuff I liked as soon as I got the dust.

I reduced my powering up during the event to only 2 Pokemon (Confusion Psychic Eggs / SlowBro both with good IVs). Now my dust is over 200k.

tl;dr

Save your dust, choose wisely.

Vaporeon with water pulse is awkward to battle against so I would consider it a good defender. The high IV make him an even better one because his CP will max out very high. On top of that it already is on a high level so I would say power it up.
Venusaur is the main Vaporeon counter so definitely a top Pokémon, especially with that moveset. IVs on attackers are not super important, since you don't want to max them out. I'd say power up your Venusaur just enough to be able to take down 2 strong Vaps in a row.
With Gyarados it's difficult. He was not a great defender before the ditto patch and now his main counters - electrics - got buffed, so his defending abiliies are even more questionable. However, he also got buffed and has the third highest CP of all non-legendaries I think. With 93% IVs his CP will be impressive. I say power up that bad boy.
Arcanine simply has too low starting CP, unless you forgot a 1 there.