One of the advantages to Manston is that it has motorway/dual carriageway all the way from London. On approaching the airport you are not snarled up in traffic like approaching Heathrow, for instance.
You might equally argue that one of the DISadvantages of Manston is that it has motorway/dual carriageway all the way TO London. I'm always amused by the way that some people describe the journey TO Manston as an absolute breeze but the same journey the opposite way as the seventh circle of hell. I don't think the reality is quite that simple. Let's be realistic - whatever happens to Manston, people will still use Heathrow. The congestion around Heathrow is irrelevant because it's simply not comparable to Manston. As for Gatwick and Stansted, I think the difficulty of accessing either of them is greatly overstated in certain quarters. Those same motorways and dual carriageways can carry people FROM East Kent TO LGW or STN where a greater choice and frequency of flights can be found. That will always put MSE at a disadvantage.
In a few months there will also be a high-speed rail link from Ramsgate.
Partly true. The high speed rail link will go as far as Ashford. Thereafter, the trains will follow existing track to Ramsgate. Factor in transfer times back to the airport and suddenly it's not such an attractive proposition. Also - and some locals seem to overlook this - the new rail link terminates at St Pancras. That allows a one change train journey from Ramsgate to either Luton or Gatwick (and in due course, I think, to Stansted).
BTW - please don't think I'm knocking MSE. I do think it has a viable future, but probably in freight rather than passengers.