If you're running pure Primaris, it's a different kettle of fish; if you're running mixed, I don't believe it has much value as the Primaris would be better served bringing tools that Veterans can't (eg, Hellblasters for anti-armour).
1) You can drop them 18" from enemy lines, instead of 12" (well out of charge range) and use Vengeance rounds for 2 x S4 AP-2 D1 shots each.
You could just use Veterans and do the same thing? There's nothing that says Veterans absolutely must drop in as close as possible. For maximum firepower, sure Veterans want to be closer, but they still kick out good firepower at range (it's straight up the same as an Auto Bolt Rifle at over half range).
2) Not only can they fall back and shoot, but they can advance and shoot each turn without penalty to stay in ideal range.
Advancing without penalty is nice; I don't personally believe that it's worth the loss of Storm Shields, though.
3) Max efficiency is at 18", rather than 12". So you are less succeptible to return fire and counter charges.
The models kicking out SIA have the same ranges, but the Inceptor and Aggressor both have 18". If you're firing at 24-30" with Hellfire/Kraken, the Inceptor/Aggressor is doing nothing which is more of a loss in firepower than a Vanguard is.
Veterans have the flexibility there. The difference in maximum efficiency is that Veterans are the same at 18-30", worse at 12-18", but better at 12". If the unit doesn't need/want to move, the Veterans can utilise Bolter Discipline against the targets that the Aggressor likes and be more effective.
I wouldn't say that this is a clear cut 'Intergressor squad has the advantage' because battlefield situation is very important and there are many where the Veterans have their own advantages.
8 Veterans + 2 Terminators is roughly equivalent in price to 8 Intercessors + Inceptor + Aggressor.
Yes, you give up the invul saves from a SS, but you get more ablative wounds, higher threat range and more mobility.
You give up the Storm Shields, but you don't, really, get more wounds because you're now open to all of the anti-MEQ
guns out there. Plasma, Disintegrators, etc.
The main advantage of this Intercessor team is that it's kind of faster than other infantry.
Simply put, Primaris are highly vulnerable to too much stuff. A unit that trades away some of their inherent advantages over Veterans (eg, the Bolt Rifles' range and AP) for some slight extra movement is likely not going to be great.
But try it out. It may work well! Let us know!