Comment 10 for bug 165952

http://wiki.inkscape.org/wiki/index.php/Frequently_asked_questions
under Question 3.6.
it states that import of bitmap will always be at 90dpi.

Easy idea to solve this problem:

in Inkscape > File > Inkscape Preferences > Import/Export > Default import resolution: 300 dpi

All my bitmaps are in 300dpi, so at least for my case this would solve the problem.

btw: Nice work, overall Inkscape is a fine software!