How to utilize multiple ask the user filters in single query while allowing for situations with no input for some of the filters.

I'm sure we can come up with something. Can you post more information about the exact workflow your user follows? My first thought would be something along the lines of creating helper fields for each filterable field, where the helper fields are formula fields, and the filter is done on the helper field rather than the data entry field. Sort of the reverse of Coach's suggestion, in a way.

I don't know if you'd call that kind of a solution ELEGANT, exactly...