Workaround to include inkscape vector graphics into libre office impress
Inkscape vector graphics (.svg) appear a little bit blurry when used in libre office impress (Version: LibreOffice 188.8.131.52, Build ID: 350m1(Build:2)), especially when text is visible on the graphics.
I think the easiest workaround is to export the inkscape graphic as a .png bitmap
File -> Export Bitmap
I got good results with the default settings (90 dpi).
The generated png can then be included into Impress.
If the png is too small, it is advisable to enlarge the vector graphics in Inkscape and then export the enlarged graphic to png.