<sigh>
As I have already demonstrated, there is nothing special about a townland, it is easy to look up the historic civil parish definition too.
My point is the word "Castleknock" is not, nor has ever been, exclusively used for the townland of Castleknock in the former county Dublin. That it applies to several different map divisions provides a plethora of overlapping areas and different definitions of what "castleknock" is. You've picked one to suit your purposes and seem almost apoplectic that anyone could possibly have a different, equally valid interpretation. Your premise is invalid to start with and all conclusions you draw on the basis of your premise are therefore equally invalid.
Regarding the property prices, the type of people you need in an area like Castleknock to maintain the comfortable status quo are being or have already largely been priced out of it. You are selling to a limited market. The population mix will very likely have to shift to a higher density model at some point, it probably already has started. In a functional market, as property prices peak they tend to attract developers who want to put more properties on large sites, why sell 1 big house for 500k when you can sell at least 5 smaller on the same site for €350k apiece? As for your markers of the desirability of Castleknock - they aren't so difficult to find elsewhere. High ranking public schools, low anti-social behaviour and close proximity to nice parks are a blessing shared by many people in considerably cheaper parts of the country. You don't need to pay 500k+ to get that - it is only a Dublin-focus that leads you to that fallacy.
You'd be one of a very select group of one that would consider me socialist, I have no intention of forcing down the price of your property and I have no desire to either. I am merely extrapolating from documented urban history of all major cities, including Dublin. Former desirable areas go out of fashion for several different reasons but being over-priced is an important factor; cheaper, newer areas opening up in competition is also an important factor. It has nothing to do with begrudgery - it is quite easy to prove. If you want to see how it happens visit the new museum of Dublin tenements when it opens. That is to be housed in a former tenement which started out life as a grand town house in an exclusive area and slowly but surely degenerated. Dublin was notorious for the worst slums at one point - almost all of them were conversions. Same processes can be found at play in London, New York, etc. and are at play in Dublin of today.
As for your spurious car analogy. The difference between buying/selling a car and a house is that the same car will cost you in or about the same price all over the country - the same house won't. They aren't comparable. Your "fake merc" equivalence to "Castleknock-but-not-Castleknock-townland" is ludicrous.