sorry, seems like i didn't understand you properly
i don't know about an app merging summaries, but i've written something similiar: i've created a mysql database to which you can upload netstumbler and kismet logs. you can export the whole list to a text file which then can be turned into a map using my own little VB-app and mappoint 2004 (not really nice coded, just quick-'n'-dirty
)
if there are peeps interested in this thingie i'll code it a bit nicer, translate it into english and release it