Not saying you necessarily have to, both can do good work. You do need to be aware of what you're getting for the points, though, as the point investment is a big one.
Note the Inceptors really don't benefit much from most Chapter Tactics anyway (they're prolly best as Iron Hands or White Scars... Maybe Crimson Fists). They're still good in their role - jumping around, delivering brutal close-range firepower, potentially plugging sudden holes in your line or grabbing an objective. They're your only mobile element, IF you replace them make sure it's by something that's mobile as well.
The Aggressors I'm actually a little more iffy on, as I'm just not sure they'll get to do their thing in this list against many opponents. They'll do well enough against melee heavy lists that don't have a choice but to get near them.
Ask not the Eldar a question, for they will give you three answers; all of which are true and horrifying to know.