Re: valkery abilities
One thing worth mentioning is that you can recast Valks until they seem to get some gear that serves them well. A high-level Valk gets a fair amount of rare gear, here's the rundown:
lvl 1 rare full plate mail and spear
lvl 2 adds magic heavy gloves
lvl 4 adds magic heavy boots
lvl 5 adds magic heavy belt
lvl 7 upgrades full plate mail to rare chaos armor
lvl 8 upgrades spear to rare lance
lvl 10 upgrades heavy gloves to magic war gauntlets
lvl 11 upgrades heavy boots to magic war boots
lvl 12 upgrades heavy belt to magic war belt
lvl 13 adds magic amulet
lvl 14 adds magic circlet
lvl 16 replaces chaos armor with rare sacred armor
lvl 17 replaces lance with rare war pike
lvl 19 upgrades war gauntlets to rare crusader gauntlets
lvl 21 upgrades war boots to rare mirrored boots
lvl 23 upgrades war belt to rare colussus girdle
lvl 25 upgrades magic amulet to rare amulet
lvl 27 upgrades circlet to rare tiara
So by the time you've got a high-ish level Valk, there are a lot of rare items, each with potentially useful affixes. Chance to cast Amp is one of the better ones, depending upon your build, decent life leech is also a plus, poison damage can help alot, cold damage or chance to cast Frost Nova are also sometimes good. The problem is that you can't tell what the gear turned out to be until you've seen the Valk fight somewhat. So you can keep an eye on her- if her gear seems to have some useful mods, and she seems to be surviving well, great. (Maybe she got some life leech on her weapon or circlet, for example.) If she seems to be struggling or have gear with a bunch of useless mods (ctc charged bolt, monsters flee, ??? depending upon your build) then it may be worth recasting her and hoping for better affixes on her rare gear.
A good Valk can last for hours, so I find it worth keeping an eye out for getting some useful gear and maximizing the skill level the Valk is cast with. A skill shrine, some +skill gear or someone else's Battle Command are all helpful and worth the trouble for a minion that may last so long.
I think in the SPF there was a description by Insane Wayne about how to tell some of the mods of the Valk gear by color but I can't find the thread at the moment. For example, a lance with poison damage is often green, so sometimes you can tell even before getting into battle what some of the mods on her gear could be. Other desirable affixes and colors that may indicate them: a Cruel lance is black, weapons with life leech are often red, white weapons sometimes have the Fool's affix, and elemental damage often colors the weapon with the appropriate color (red fire, blue cold, yellow lightning.)