"I am interested to know where people such as Ruth Archer & Anahata think that promotional hype fits in to the model of sustained careers in folk."

"Sustained" is a very significant word there.
Undoubtedly spending that sort of money gets you some fame and recognition. It's likely to create controversy in the folk world too, in fact it has done when that approach was taken, and as Dave says, it doesn't ultimately last.

Unless you're very lucky, talented and organised business-wise, there's a good chance you can blow a load of money on promotion and not get back what you spent. Also you may be famous for five minutes, then somebody else will be the next Big Thing and you are nowhere, and worse still you are "so last year!".

You can get lucky. I was just reading the article about Chumbawumba in fRoots - on the strength of one song in the top 10, they toured the world and did lots of stuff they'd never be able to do otherwise. They also kept their heads on and knew it wasn't likely to happen again. Since then the money earned at that time has given them more freedom to do what they want musically. I'd love to do that - but we don't all get into the top ten!

"imho, [hiring a PR company] would make a difference and I'm not sure that it should"
It would make a difference, but it might not make enough difference to pay for the cost of doing it. In the folk world, for example read Jacey's Why you don't need an agent. And again the effect wouldn't last unless you had some real talent that people wanted to hear anyway.

One of the things that appeals to me about folk music is that there's something real and timeless about it. It's about playing the music I love, and hopefully infecting others with that enthusiasm, and introducing it (when I get the chance) to people who've never heard it before. Not about playing whatever will maximize profits - if I wanted to do that I'd play C&W in Norfolk pubs!

I'd much rather build a reputation slowly and feel I've earned it. It's more likely to stay that way.
But I can afford to: my life doesn't depend on it.

Anahata