That said, I have met engineers who felt their work was 'worth more' than that of a 'marketeer.' Which is not true. But that applies in the general case and not in the specific case.
"I've always thought salary has more to do with perceived class of role in society opposed to value created (in most companies)."
Actually that hasn't been my experience. At least in the SF Bay Area salary budget was managed much as I would imagine a sports team manages their salary budget, which is to say the amount of money the company could spend on salaries was $X and the required business revenue was $Y and the required margin was %Q for everything to 'work'. If the ratio between $X and $Y wasn't there you figured out changes needed to get it into shape. Those challenges could be 'time to ship product' (an engineering problem), 'market visibility' (a marketing problem), 'sales' (a sales problem natch), or sometimes 'cost of goods' (a structural problem). You allocate your $X salary budget to 'fix' the issues.
Class and societal role really never enters the picture in those cases.
I suspect it's also a matter of company stage (I'm predominantly early stage). If I were given $1M to start a tech company, I wouldn't hire any pure marketers. I'd hire engineers who have proven that they can design products.
I think the problem I have with marketers is that it divorces product definition from product construction. In my experience the best products come from the two being as close as possible. Ideally in one person.
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The truth is though that most of the best engineers I know are some of the worst at marketing. They can have a great idea and great execution, but they can't effectively sell people on it, and they often simply think people will automatically buy it because it works and provides a useful service. Rationally, that makes sense.
Unfortunately, that's not really how things work most of the time. If you've started a business, you should know that sales and marketing takes work; even if you have the best product, it's not useful if nobody knows about it, or if it is associated with the wrong thing. That's why marketing is valuable.
There are also examples of sucessful tech companies with little to no marketing department (Craigslist to use an old example). I don't think he same can be said of the reverse.
"... it's clear that plenty of engineers play a marketing role in addition to their role of 'shipping'."
That is an interesting statement to make. Some really great marketers that I've met started with a CS or EE degree, and some really great engineers I've met started with Economics or physics degrees. It isn't the degree that defines them, it is where (and how) they add value to the goals of the company.
In the 'way back' times there was a video format war, it was called 'betamax' vs 'vhs'. Betamax was a better engineered standard, VHS was a better marketed standard. Then there was the "OSI" vs "TCP/IP" network wars, OSI was heavily marketed, but TCP/IP was better engineered . Word vs WordPerfect, Lotus 123 vs Excel, Firewire vs USB, the road is littered with "products" and "standards" where either good marketing or good engineering determined their success or not in the market place.
Generally it seems that if you have two competitors with equivalent engineering teams, bet on the one with the better marketing. If you have two teams with equivalent marketing bet on the better engineering team. Either marketing or engineering can cover for some weakness in the other team, so yes, I value them equally.
That you don't suggests you haven't experienced really great marketing. There was a great post by Joe Kraus (Google Ventures) on this . Something to think about.
 Some (many?) would argue that OSI was over-engineered, but either way it was heavily marketed.