I've replaced them over my
display rather often. 6 months'ish
Partly because I would get bored with the color and partly because they seem to shift color.
I cant say about the hamys but Phoenix and Aquaconnects start turning more blue after 6+ months. I dont think they lose intensity as much as they just shift color...
Now over my
frag tank, I plan to just use a up a bunch of old bulbs I've had sitting around. Until they just get really dim or burn out.

...For the same reason you said, Uber lighting isnt my concern.
Heres a good
read if you havnt seen it yet.