A few points noted-
Sector A is no better than other sectors, people who live there just think it is. There is no avoiding that some poor souls on D have major problems with their villas, roads, deeds, etc
The area has improved, no thanks to Masa, but the commercial centre on B leaves a lot to be desired regarding cleanliness. A lot of areas look neglected, though local gardening groups do their best. Only 900 0f the 4500 villas have owners who pay ibi (council tax), so no surprise the council never has enough money.
The villas are very cold in winter due to the construction with no insulation. Yes its nice to have double glazing and central heating-if you can afford it.
If you have any mobilty problems, or need frequent trips to the doctor, the D is probably not a good idea.
To the couple retiring here in their mid fifties-you will need private health insurance, which may not cover any existing conditions. The couple you quote who go back to UK every three months so see their GP, are committing fraud, as they have left UK to live here permanently, and are now no longer eligible for NHS care, which is residence based. Income tax, apart from government pensions eg civil servant, military, has by law to be paid in Spain on all your income and savings in the UK.. It is not a choice and you do have to register on the Spanish tax system, whatever anyone says-plenty of info on web. Get a properly qualifird tax accountant or you may pay too much tax.
I f you have an income of 1800 euros per month, to live on in Spain, you are indeed fortunat