I am not sure if WOTA should be more of an independent item, or if it should stay as a cheap mid game alternative for Hextech until you reach full build.
Cheap mid-game item, 100%.
Spell vamp currently has 2 main issues for why you wouldn't get it:
- if you're so ability-reliant you're going spell vamp over life steal, running OoM is really, really bad. Mana sustain > HP sustain during the lanning phase of most champions that could make use of spell vamp.
This favors a cheaper item for fitting spell vamp into a build as an alternative, as there's a pull for another stat first and a clear drawback.
You'll also generally notice the vast majority of spell spell-vamp users are manaless or can utilize manaless abilities for spell vamp:
(Jax's Grandmaster applies on-hit effects and is a 100% in-effect passive skill, Nunu's passive allows him to cast a manaless spell after so many auto-attacks).
is better.
Sustained damage champions rely on life steal to sustain through a fight come late-game, allowing a glass-cannon build the durability it needs to be appealing (rather than going bruiser build on everything like you would in a typical RPG).
Hourglass offers a burst of defense for burst casters, so they can burst and then have the CDR window they need to burst again (or counteract getting bursted).
Considering the power Hourglass can offer, it's fair to say it's better than life-steal in several scinarios, a 
with Hourglass can fairly easily cause an Ace, a Fidd with spell vamp will probably tend to be underwhelming.
Anyways - if WotA is going to appeal to AP champions as a source of in-combat defense or lane-sustain, it needs to be cheap enough to merit diverting to on occasion within a 
path.
On to your suggested change:
New [2935 Gold ]
100 AP, 10% CDR, 20% Spell Vamp
This seems more like diss-incentive to get the item over a minor buff.
The average champion in the average game of LoL ends the game with 11,000 gold - which works out to about 1k for boots, three major 3k items, and 1k in the bank when someone's Nexus explodes.
So - there is little value in an item being "slot efficient" when it comes to LoL, because you'll rarely run out of space before a game ends.
Which is the only advantage stat-sticks you can get with base item (or mostly base item) components really accomplishes.
Otherwise, you're pushing another item that offers AP and CDR 435 gold down the game time to it's completion, setting access to it's unique passive/active effects further back.
The 10% CDR boost just doesn't strike me as very worth it in this context, as the 435 bonus is 20 AP in the most cost-inefficient item tier of cheap base item components.
CDR in particular is a pretty awful stat to tack onto items willy-nilly, because it becomes useless when you hit the 40% cap, which isn't particularly hard to reach in any particular build. Sometimes it requires CDR boots or runes, but if you really want CDR maxed on someone like that scales extremely well with that stat, why Not get CDR maxed ASAP by using boots and runes with CDR on them while pushing things like M Pen into later-game itemization?
due to their AD Ratios/ Auto attack dependencies
HOW DARE YOU!?
now tho. I would not buff the CDR as it would make 
for that, 15% CDR.
to the rescue
and 
. I would love to have that and 
at the same time.
The problem with auras is that they're "invisible power." As an aura lover I hate that it's not a healthy thing - it feels useless but is actually quite powerful.
