" The romance, though, is of our own making - the truth is rather prosaic."
Port Ellen (PE) is a good whisky and slightly less "characterful" than an Ardbeg or a Laphroaig. I do agree that the cult status of PE is reinforced by being an Islay whisky. However, a whisky don't get a cult status simply because it is a mothballed distillery. Some close or silent distilleries, such as Glen Keith will never reach a cult status, because the spirit was an average single malt.
Brora is now very sought after, because it is a very characterful whisky, with some similarities to the best Ardbeg and Bowmore from the 1970s. I do find most of these whiskies excellent.
"The interesting thing is that despite their current cult status, both Port Ellen and Brora were made as blend fodder. "
I think that the historical content should not be ignored. Until the end of the 1980s, very few whiskies were sold as single malts (e.g., Glenmorangie, Glenffidich, Glenfarclas) and the primary objectives of the distilleries was to produce "blend fodder". Brora and PE were closed because of overproduction during that period and the production of these distilleries was replaced by more modern and economical distilleries (Clynelish and Caol Ila). Diageo only started to bottle the Brora and PE in 1995+ and it is only then that whisky enthusiasts started to discover them as single malts. Brora will probably never reopened, since renovation would cost a lot of money and that the production costs would be too high.