Your queries look fine to me, although I would use a combination of AddFieldDelimiters and in-line variable substitution to keep them a little more manageable. AddFieldDelimiters is nice in case you want to apply your script to different workspaces where the query 'punctuation' on the fieldnames is sensitive, without having to change your script.
Back to what I still think is your issue, I don't think it is enough to simply define the query def property - I think you have to use 'updatelayer' to commit the change to layer properties in the map. Look at the Layer object webhelp doc...you can do something like 'get' the map's current layer properties with your layer object created in your script, then 'replace' or update the map's current layer with the one you modified in the script - make sense now? Conceptually, it is like dragging and dropping layers between maps (an easy way to copy layers from one map to another) -- if you change the layer props in one map, the changes are not reflected in the other. But you can 'drag and drop' to the other map again to sort of refresh the layer, reflecting the current modifications.
Most importantly (in this conceptual example), you will have 2 copies of the layer in the map you 'recopied' to, the 'old' one refecting the original properties and the 'new' one you updated or changed the properties on. You have to remove or delete the old feature layer from the map...so instead of adding-new-removing-old with your script, the analogous operation in your script is to use 'updatelayer'. That's why you need to 'read' the position of the layer in the map and 'stamp' it with your modified layer object.
Hope that makes sense - you don't have to use layer files or a source layer from another map.
Enjoy,
Wayne
