Vrocks aren't that complicated really. Their special abilities can really get on your nerves, sure, but none of them are overpowering (except for one):
Greater Teleport at will means you will want Dimensional Anchor or, better yet, Anticipate Teleportation. You'll probably be ambushed at some point, and some of the baddies will probably be able to escape at other points, but it's not as if this ability will outright kill your party.
Mirror Image spam: any spell which causes multiple attacks all at once quickly counters this, as does closing your eyes combined with something to help you pseudo-see, like the Blindsight spell,
Spores: Bless, Remove Disease or Neutralize Poison; the latter provides immunity over a time period, so if you care enough about the spore damage, that's your go-to,
Stunning Screech: can get aggravating if there are many of them - Silence stops it cold.
Dance of Ruin: this can normally be disrupted by just killing the buggers before their dance completes, so be glad if multiple Vrocks waste 3 rounds to set this one up,
Summon Demon: Yes, please, do this! Waste a full round for a 35% chance of actually doing something! Sure, if it works, your party might be all "uh-oh...", but usually, this ability sucks except if used before combat even starts.
Fly speed: you ought to be used to this by now. Get a fly speed of your own. Remember you can trip flying creatures. Tanglefoot bags and the like also work well. Your Druid might want to prepare Wall of Thorns and trap the Vrocks in it, so they can't fly away.
Damage reduction: yeah, well, pack Good weapons, or the Bless Weapon spell, as DR 10/good can still do a lot of damage prevention at your level.
Resistances, immunities, and SR: none of these are of much consequence - SR is too low for the level, and energy damage shouldn't be a go-to when fighting outsiders, anyway.
Telekinesis: this is very open-ended and can get very bad, if your DM uses it creatively - this is really the main danger when fighting Vrocks, since they get it at will. Nothing to be done here except killing them quickly.
Vrocks can dish out some OK damage in melee, but they might still have trouble hitting a good tank, and their AC is subpar for the level. Focus-firing individual Vrocks in melee thus quickly brings them down. So I wholeheartedly recommend melee combat unless you have no good way of dealing with the Mirror Images. Stoneskin (if you can afford it) makes melee even better, since Vrocks can hardly scratch you when you have it up - they rely on multiple low-damage attacks. Remember that Vrocks have no True Seeing, so illusions are certainly another possibility. Suggestion and Charm Monster are options, since Vrocks only just have OK Will saves.
