Thanks for the post and for the great suggestion. We’ve definitely been asked about this before so I have added your vote in support to our internal tracking.
Taking a step back, we’re well underway in creating new, native desktop apps based on our Balsamiq Wireframes engine. Those will be shipped later this year and I mention it as it’s more likely that requests for new or improved features will be considered for these new versions, than for the existing Mockups 3 for Desktop app.
I should mention that we’ve already shipped a couple of products built on the new engine, one of which is Balsamiq Cloud. One relevant improvement in Cloud is better quality export to PDF. We offer a free trial for 30 days (at link above) so I’d encourage you to try out Cloud and see if the improvements in PDF quality meet your need to some extent? You can easily get your Desktop projects into Cloud as both apps. use the same file format. See: Managing Projects
Get back to me if you have any other questions, ok?
All the best,