You bring up an interesting point that reminds of the many threads I've seen that go on about the further normalizing of ultimate mana costs to 100.
Admittedly you appear to going one better and critiquing the whole of Veigar's mana costs, which are indeed one of the higher costs (when leveled up).
As someone's who played Veigar quite a few times, I understand the concern for "outdated" mana costs, as without mana items the pool is exhausted quickly (hence when tear into AA staff is so common).
This is the reason I do the building of him that tried to minimize his cost, while trying to get the most usefulness out of my mana, that is to forgo leveling his dark matter beyond one, because the level up damage and cooldown is insignificant in comparison to the utility of his baleful strike and event horizon (Dmg + AP + Stun).
Now, as for changing the costs, I believe that it is possible to make them more desirable and less famishing, particularly with Dark Matter (aka, a reason to level it). The only problem I see with such changes is that likely something would have to be taken out of the abilities to compensate (I do not mean the passive), and I say this because Veigar has the unique quality of getting AP for kills, therefore i theory his abilities have the potential to be more powerful than others of a similar caliber, which they certainly can be. Personally I'd rather not see his abilities gutted just for mana costs, but if its only a minor change I could deal with it I suppose.
Now as for the passive, I kinda of miss his old passive, but think it too powerful to implement without serious consideration to the power level. If you don't know what it was it was called Entropy, and it applied a debuff to his enemies when struck that "stole" AP. Now a passive that gives him more AP is a double edged sword, as further gutting would have to occur for the power.
Personally overall I think he's fine as is, but would a tuning be uncalled for, not really. I think the costs for his abilities are fair because the scaling and utility they bring, especially with a mana regeneration passive of any description. With that note I find the passive acceptable, but would something else kill him, no. I hope that was somewhat insightful.
