I like to try and change my NO lamps at least once a year (some folks recommend as little as 6 mos), and I'd definitely do that when running a single. Aside from loss of intensity, fluorescent lamps also tend to change their spectral output as they age (phosphors wear out). This will vary somewhat from bulb to bulb.
I didn't realize that Hagen had changed their lineup. They only had four lamps to choose from back in the day -- Power-, Aqua-, Flora-, and Marine-Glo. At least, that's all my LFS sold. Thanks for the heads up. Nicely put about color temp etc. also. I doubt I could've said it better.