[Suhiir]

Almost all the current UAV's are size 0 and have a significant EW rating. While they're reasonably hard to hit with radar guided weapons or MPADS/SAMs (a recent change causes Area SAMs to no longer fire on them) they're still fairly vulnerable AAMGs, if your opponent is mechanized they'll have a LOT of them and in spite of what the game tips say the chance to hit is about 8% so you can pretty much guarantee that if 12-15 AAMGs fire at a UAV it'll go down.
In my experience Spotter Aircraft/UAVs are of limited value (especially since they're very expensive units) since the AI always has a significant number of AA weapons. The best use I've found for them it to fly them over your own positions, well back from the front lines, to draw AA and deplete MPADS so later in the game you can get some use out of helos/aircraft because they also fall like raindrops to the AI's AA.
Of course if you're playing against another player who forgets to buy, or buys minimal, AA the situation is entirely different.

The "God View" actually simulates UAVs reasonably well. Increasing the Vision Rating of units will make them more expensive (particularly if you go for TI/40+) and may cause some balance issues since if all an OOBs units average 20% more expensive due to increased Vision ratings you may find yourself running out of ammo, if not necessarily units, before a game is finished since the units you do have will have to shoot/kill more to make up for the lack of units overall.