I believe the reason that none of these attempts work is the following. Some attributes cannot be assigned a variable value. This includes both 'style' and 'visible'.
For example, the following attribute assignments do not work.
Code:
<Image Name="Icon1" ScrollExtent="40,40" Size="40,40" Style="(Var)" Var="MyStyle"/>
<Image Name="Icon2" ScrollExtent="40,40" Size="40,40" Style="MyStyle" Var="false" Visible="(Var)"/>
I have been working on making archtypes work in the groupmember window as well but I think as long as the above is true it is impossible.
It would be nice to have a list of attributes that cannot be assigned a variable. It would be nicer to have this fixed :-)