Hi,
I have same question in Question about Solr Search and pages priority - #5 by Aleksey2610
I want to add weight to tag in search (for example, pages where tag with search word occurs will be higher in the search results). I think it may help (but my topic in progress).
update: In you case may be help add filter to search (if u want search only in tags and not in page title, descrition and etc)