I've worked with a number of monitoring tools over the years, and besides basic upgrading and patching stuff, the most important thing is that staff actually uses the tools, and continually ensures that the tool monitors what is necessary, and just as important, doesn't monitor what is not necessary.
Making changes needs to be easy to do, and reaction times, in case you have dedicated staff to do the changes, need to be fairly prompt. If people discover that the tool is always full of false or stale alarms, they will tend to not look at it anymore.
Also, when evaluating tools, look for a vibrant user community where people are allowed and encouraged to exchange ideas