SCUDs for WinSPMBT?

[Marcello]

That'd be overkill

Well not really: read again carefully:

multiple launch rocket systems, long-range artillery pieces

Which we have in the game.

air and missile defense weapons

Things like S-300 and Patriot batteries, which again we have in the game as on map assets.

Note: I am not arguing it should be added in the game. Russia has just a dozen of free weapon slots left, it would not be economical to add a weapon which is just barely within the game scope.

now i wonder what's the use of the SCUD with its accuracy

Nuclear strike capability for Front/Army commanders. FROGs did the same for divisional commanders. When you are packing a bucket of istant sunshine accuracy is not as important (unless you are going after hard targets.)
Of course if you are shooting at city size targets, and some military bases are big as cities, then you can get some mileage out of conventional warheads.