WMI vs. SNMP and Reliability

Hello,
I am attempting to monitor approximately 20 windows 2003 based servers across my organisation. I have them setup to use WMI. The problem I have is that it seems that most of them have "no status" - or rather the grey circle with a line in it. Occationally I get a green light on one or two of the servers, but generally they have no status, and the infomation is out of date.

But, when I configure and use SNMP it seems to update reliably, and quickly. The problem with SNMP is that I cannot monitor the windows logs nor specific services.

Is there a known issue with WMI or am I doing something wrong? I'm not getting an accurate reading even from the server the application is installed on. Im also using DOMAIN\UserName for the user.

Any comments / reccomendations would be appreciated.

Thanks
Gareth