My mini doesn't detect much network neither... I think it has something to do with the wifi antenna.. because i did swap the wifi card with another known working one and still the same issue.
Since then, i never used the wifi on my 06 intel mac mini anymore..
Macbook 6.1 - Core 2 Duo 2.26Ghz, 8gb ram, 500gb 7200rpm HD
Mac Mini 1.1 - Core 2 Duo 2.16Ghz, 2gb ram, 320gb 7200rpm HD