We deliberately do not do this. The icons shown in the project tree are meant to reflect the type of project item. Thus VIs show the same "I am a VI" icon, not their particular icon. The only time you see a different icon for a VI is when it really is a different type of thing, for example, a global VI or a control VI. But the difference is always on type. For build specs, the icon reflects the fact that the item is a build spec and what type of build spec (EXE, DLL, etc). This is a conscious decision to make it clear what information is reflected by the icon for any given project item. If some icons reflect "type" and other icons reflect "this specific thing regardless of type", the project tree becomes less coherent overall.
