Does Support Matter If There Was 100% Uptime And Scalability?

Does support matter if there was 100% uptime and scalability?

Our team has been developing scalable sites since 2004. We started renting servers from Layeredtech then, since they had good reviews and they were still good until we migrated away from dedicated server land. Although we have systems administration backgrounds, it still took time away from developing software in order to administer the servers (look over logs, backups/restores, performance graphs, hardware failure, etc). Having said that, one thing I've noticed is that customers are usually happy if servers are always running and running fast.

To get rid of the systems administration part we tried Mosso (they had just released, great support but a lot of problems), we tried mediatemple's grid (also had a lot of problems), couldnt try EC2 because of persistent storage, and lastly we are currently using thegridlayer (it lags, the initial request takes about a second to display a page with no load on the server).

The next things to try were VPS then managed dedicated servers. We decided to try VPSes so we can isolate sites from each other and add VPSes as needed for specific sites. So I got a zone.net and they were running fine until they had a problem mentioned here. People recommended them because they had fast servers, now is the opposite because of this one downtime.

So finally, my questions:

1) how much do you think support is needed if your hosts provides fast servers and 100% uptime?

2) What measures do you take (if any) to verify the host's procedures such as backups, company size, profitability, etc?

3) How do you verify that a host is not overselling before buying a hosting package (assuming shared or VPS)?