Argentina would need to sort out refueling problems for its aircraft before they'd even try and hit Ascension, and as its been pointed out, they needed to deal with the IFR for their Mirages, Daggers and Skyhawks, as well as more refueling aircraft.
If they had managed to get those Exocets the French stopped (Thatcher must have had something to do with that), and managed to convert some 707s to tankers (Aerolineas Argentinas had a pile of them in 1982), then Argentina could have easily been more effective, without the Vulcans.
Worst scenario possible here is that Argentina invades the Falklands, the Brits immediately say they are coming, and Argentina decides to hit Ascension to slow them down. This risks the US getting into it, but if it works Britain would have a much tougher time putting a force at the Falklands.
The Argentine Air Force would not be so stupid as send bombers without fighters, so they'd get 5-6 707s flying as IFRs, then send Vulcans and Canberras, along with Daggers to cover their backs, and refuels them en route. Flying over Latin America is not really a problem, as many Latin American nations were sympathetic with the Argentines.
Result is a hit on Ascension which does do some damage. Assuming the Argentine AF has 8-10 Vulcans and its 14 Canberras, which is a fairly large number of bombs dropped on the base, though the Daggers would be busy indeed trying to stop British aircraft.
The knowledge of Argentine strike capability forces the Brits to crash course their VC-10s, and tell the Argentines they will respond in kind. Better IFR however could allow The Victors would work as a stop-gap, but you couldn't do that more than a time or two before they run out of airframe life. You'd get air battles thousands of miles from home by both sides, which also forces both to watch their backs from a long ways out.