Even if you had zero other magic damage on your team and you're getting incredible farm, I still would not agree with you. Aghs costs 34% more and doesn't increase the damage of gale. Gale+Nova damage with veil is almost the exact same as Gale+Nova damage with aghs, so you're potentially doing the same damage on multiple targets, but for much less money. Again this is not even factoring in the damage increase to your team.
Also aghs only reduces the cooldown of nova at level 16 (100 seconds to 60 seconds), so why rush something that you're not even going to get the full benefit out of until later in the game?
Veil lasts 25 seconds, usually helps every person on your team, costs less, and can be used if a teamfight is being forced within the 100 seconds veno ult is on cd.
In Conclusion: Poor man's aghs my ass.