I just discovered (thanks to an academic colleague) a very useful dissertation available online. Elizabeth Morgan’s dissertation (UCL, 2010), Delivering Value for Money: why and how institutional archives should market themselves to their internal publics, explains why internal marketing/advocacy is absolutely essential. She includes lots of great realistic examples of what can be done, drawn from business and university archives. The work was awarded first prize by the Historical Association and hence is available via their website.
Delivering Value for Money: Internal Marketing Matters
The Special Collections Handbook 
Hi, I realise this is now a very old post, but just to let you know that the link to the article on the Historical Association website no longer works – the article does still exist but at this new address: https://www.history.org.uk/resource/4795. Thanks