Okay - sorry that this is considered inappropriate for this list. It is commercial and Windows only (at the moment) - but I thought that it may be useful for some users searching for a solution to this problem. I can't find any stats on it, but I assume that the majority of Inkscape users do use Windows simply due to its ~70% market share (according to w3schools)?
It is written using the .net runtimes so it would need to run with Mono, and so there is some work to do there first. Whether it is worth investing the time depends on feedback from the Windows version and how many users need this solution. I'm also not against making this open source in the future.
It is actually quite different from posterazor, which does not preserve vector graphics or text into the PDF - nor can it create PDF layers. So I feel that this tool is filling a useful niche until Inkscape can support multiple pages.
Anyway, thank you for your time - I won't post again on the subject.