Just comparing WotA and Hextech gunblade, I hardly see a reason for WotA unless im playing support or something. The gunblade has 10 less ap but offers a very useful active, 40 ad and lifesteal. Pure ap ofcourse dont care for ad or lifesteal but still then they get the active for 10 less ap. WotA does costs less but being there is only 3 spell vamp items, both the gunblade and WotA should be imo, fairly strong in their own way. Nothing big where the item dominates over others but something so that it offers alot like hextech gunblade. Maybe slight ap total increase or larger spell vamp.

and a side note..... FIX DARIUS'S ULT. Think everyone agrees with that by now except the few who enjoy their easy pentakills.

1. Auras do not make an item a "support item".
2. Will of the Ancients is still very good for mages, it is just closer to its actual value in cost right now.
3. Spell vamp has been found to be problematic in large amounts; therefore, the stat must remain very limited with only a few exceptions in champion kits that include it at the cost of a drawback somewhere else that balances out the effects.

4. Darius was "balanced" when he first came out. He was actually "underpowered" when he first came out in games where all players play competently. By design, Darius mostly stops scaling as soon as he hits level 13 and his damage abilities can no longer be leveled up. After this point he becomes very item dependent, and the lack of defenses/escapes/steroids in his kit coupled with his melee range make the gold and item requirements to keep an advantage in durability and damages astronomical.

Darius will always fall off eventually, and unless the rest of his team is a lot stronger than yours and has racked up a large gold advantage because of Darius, his presence will eventually cost his team the game. Darius is simply too useless later on to justify a champion slot on a team. He is a liability more than a help.

same spell vamp amount for 2/3 the price

If you've got some support whose abilities scale off of AP, such as Lulu, then if the AP carry has WotA, they become better at healing/shielding. It seems many supports have AP-scaling damage abilities, so the damage bonus is actually greater than just 10 AP, and it gives indirect defensive bonuses, too.