Right now, the only change one can do without losing the exif data is the image
rotation. This means that for resizing etc I have to use another application
(like convert or the GIMP).

Exif data should normally not be lost, the same way the IPTC data already is.

If you want to be really correct, you could change or delete the appropriate
exif tags that are affected by the image change. (For example change
PixelXDimension when the image has been resized.)

But there is no need to throw away things like the date, the camera maker,
exposure time and so on.

Other information: