Melee warlocks, accuracy and metamagic

[Shinken]

I've been thinking about accuracy boosters and eldritch glaive. Spending feats on Weapon Focus is usually considered a waste, since it's a small bonus, it's a boring use of a feat and there are several ways to get +1 to accuracy (a +1 weapon costs only 2000gp and some change and it also gets +1 damage). However, for melee Warlocks, I think it's an acceptable use of a feat.
Since eldritch glaive targets touch AC, a +1 increase in your attack bonus is more significant - 95% accuracy is a very possible goal even for a mid-level melee warlock. Getting a +1 enhancement bonus on eldritch glave is a lot more expensive, requiring an amulet of mighty fists or beast gauntlets. Therefore, I believe Weapon Focus (touch attack) is a potential candidate for your 6th level feat if you took Weapon Finesse at 3rd (or even at 3rd if you are a Str-based warlock, though I don't think that's a very good idea). You can retrain it when you get more money a few levels later, but even with an attack stat of 20 that bonus is not going to be wasted.

I've also been considering how the few metamagic Warlocks can use could change their builds. Sanctum Spell is interesting because it could allow you to Quicken/Maximize invocations one level earlier. Born of Three Thunders (plus Mark of the Dauntless/Quick Recover/Favor of the Martyr/Third Eye Clarity/some other way to avoid being dazed) + Frightful Blast could make you target all three saves in a single attack. Of course, Frightful Blast is awful. The point is that Born of Three Thunders is something you can apply to your eldritch glaive and it debuffs better than most essences - meaning that +1 accuracy is not only buying you a fistful of d6, it's buying three debuffs.

[Malroth]

It's still a very Poor Feat, Even for a Glaivelock.
Glaivelocks most effective use is for battlefield control so they benefit from many of the same Feats as Reach fighters, Combat Reflexes, Knockdown, Willing Deformity Tail, All provide Substantially better use of a feat slot than boosting a usually 80-90% accuracy attack by an additonal 5 points

Clawlocks are much more in need of Accuracy than Glaivelocks, but even they have better options. Improved Natural Attack Claw, Rapidstrike, Beast strike and Knowledge Devotion

Of course Your Invocations will VASTLY outshine your presence in melee even for a Melee lock of either variety, A zombie Ettin easily creatabe with "the dead walk" the same level you get it will be a better melee combatant than you will ever be and Relentless Dispelling Does Far more to lower enemy Touch AC than any amount of Weapon Focus.