You can only deploy a small number of AWACS at a given time. They're very costly. They need escorts. AWACS can't be everywhere. AWACS cannot fire missiles at incoming cruise missiles.
Now, if the Su-30 MKI can detect, track and shoot down incoming cruise missiles the AWACS can be freed for other important duties such as Air Dominance. Besides, all forces are moving towards network centric operations. The aircrafts can feed and recieve feeds from other systems.
The more sensors you have out there - the better are chances of your survival.
But a "mini-AWACS" due to the shorter range of radar, also exposes you to enemy A2A missiles, as well as their fighters, whereas the AWACS would not be in the same immediate danger - Either way you will have a number of fighters in the air, but when protecting an AWACS, they have the advantage of keeping their distance and still detecting the enemy.
Also, with the smaller range on a mini-AWACS, you would have to be pretty lucky to be in the proximity of a missile launch or flight path to detect it- so utilizing that capability for tracking missiles seems pretty iffy and left to chance.
Sensors are fine, but you are talking about redundancy, rather than a qualitative improvement in the data received, and at the risk of being within range of enemy fighters and ground based AAM's. Some of the newer missiles actually track the radar in AC, hence the desire to be able to fly your fighters "blind" while data linked to a dedicated AWACS platform that would not be under risk due to greater range. There does not seem to be any major advantage to having a "mini AWACS" that decent coverage from dedicated AWACS platforms cannot provide or surpass.
I'm looking at this in the context of the Indo-Pak theater - where, in order to detect any missile launches from Pakistani territory, Indian "mini-AWACS" fighters would have to come within range of the Eeriye, leading to detection and measures against the Indian fighters before any missile is even launched. You risk your fighters I would think, when the same detection, or even better, would have been performed by your Phalcons.