I felt similarly regarding MS SBS 2003 - It was a 'huge risk' to have a single server that served so much - I made it worse on myself by (shooting my foot) at only 4GB of memory. But it ran,..daily,.. only one 'failure' which was a virus and I may have been able to resolve it without wiping the system. But I choose to as a precaution.
But that SBS box ran for nearly 6 straight years with very little day to day futzing. We did have downtime,.. but there isn't anything that I could do about the Windstream hub down the road being under 5 feet of water. We were running,.. just no internet.
Still like the SBS model - though in my new office it doesn't work since we have nearly 300 people.