Why don't you use the method described by bdh?
This is the result:

coming from those files (they are magnified to double size):


I think that your heights seem to be steps, instead of slopes (I don't know how to explain better). The transitions in the grey scale are too "hard" instead of soft transitions (they must be similar to clouds), leading to "plateaux" instead of mountains.

Another point is that it seems to me that you distribute the different ground types in too small parts. You should cover larger areas with the same ground type, to give the map a better aspect.

I hope this will be of help to you.
Best wishes!