Calc is currently representing a boolean value either by "true" or "false" characters lists as in the below example :
<table:table-cell office:value-type="boolean" office:boolean-value="true" calcext:value-type="boolean">
<table:table-cell office:value-type="boolean" office:boolean-value="false" calcext:value-type="boolean">
Maybe you could use "1" or "0" characters for that.
This would descrease the size of the XML stream to be parsed.
This is defined by ODF and not by us. Read section 18.3.3 in ODF 1.2 part 1.
I posted a comment to the "office-comment" mailing list of the OASIS Open Document Format for Office Applications technical committee :