My parents paid close to 20% interest on their mortgage as was common in the late 70s / early 80s. Dad was hammered on income tax and paid over 50%, again as was common at the time. Rates were charged too as were a variety of other additional taxes.
People in this group have paid their way already, if they have a disposable income now, I think they have earned the right to have it left alone.
Like the OPs mother, my parents have added onto their house over the years, developed a lovely garden, etc and I think it would atrocious for them, as pensioners, to be expected to fork out a large some of money in property tax.
a low income pensioner, in central Dublin in a 4- bedroom house worth 650,000 close to bus links and rail links all subsidised by public transport"
Even if a house IS worth this, it is not active income so are you suggesting that people should sell the fmaily home in order to pay? Also, why the positive discrimination against those who live in the city and therefore have access to better services? They paid MORE for their homes in the first place so that they could avail of said services, they've already paid extra!