I'm not sure what is causing the problem you are having but I can say you should not set this to false:
<add key="CombineCSS" value="false" />
it should be true otherwise none of true other settings will have any effect.
Note also that in medium trust hosting it could be issues with theme.skin file because in medium trust it cannot use the theme.skin file from the skin folder instead it comes from App_Themes/Default/theme.skin for ALL skins so if the skins need different settings there it will be a problem that cannot be solved in medium trust.
For example artisteer skins need different theme.skin settings than other skins and even Artisteer skins made in Artisteer 2.3 requires different settings than Artisteer 2.4. So whatever skins you choose for indivudual pages need to be skins that need the same settings.
Hope it helps,