Most of the time, if you invest in one of the big IV investments, you're losing out on a core world during V. It's a cost-benefit thing. There are sometimes when Alais is worth it. There are other times, when you're trying to get multiple Core Worlds, where it's not.
This, one thousand times this. The sector 4 cards can be very good (Queen Alais and the Worldship come to mind immediately), but they're not game breaking. The players who don't get to go first in sector 5 need something to help keeps the victory points totals roughly equal.