Good comments. The real questions are;
Is a longer runway needed - Yes
Will fleet consolidation improve Aurigny's finances - Yes
Will the business case add up - probably not when you take into account higher airport operating costs and buying in Medivac
Would this improve Alderney's economy - No
Will this provide higher flight frequencys - No
Does this reduce fares - No
Is there the money to do this - No
Also your 55 pax payload is for a perfect day, dry runway and wind straight down it. An average winter day is 37. A bad day = no flight.
However, to future proof the airport, yes it should be extended.