Derfred,
In theory, at least, a full airep should be transmitted if the symbol is on a chart.
As for "writing it down", many moons ago in AU, there was a union directive that, if the pilot did not precede the transmission with "airep" or "airep special", as required by AIP "radio procedures", the ATC person would not write down the wind and temperature and any other remarks.
As to what happened to airep information once transamitted, on the flightdeck, that was always a matter of great speculation, not all of it repeatable in polite company.
What was done with it?? It certainly never seemed to have much influence on forecasts, and I suspect BoM treated it as "unapproved information".
Was it useful, too bleeding right, it was real info., as opposed to a (particularly) wind forecast from BoM computers. Is it still ???
It is true that there has been a huge improvement in almost real time met. in the last 20 years, in the real world I rather think an airep is a historic anachronism, except when you are doing ATP Air Law.