The spectrum isnt as important as PAR though. I used to think otherwise, but as it turns out, the PUR of most bulbs tends to follow the same ratio as the amount of PAR. Simply put, the spectrum could matter less. As it turns out, look at the spectral graphs... a 6500K has more actinic in its output than any other bulb (maybe one or two exceptions, not sure, but rare if that), even a 20,000K... you just dont see it because of all the warmer spectrums. A 10,000K is pretty similar. Look at Sanjay's setup... all 10,000Ks, and plenty of color. There is loads of blue and actinic in that output. 'Supplimenting' bulbs is pretty much for our own visual tastes. If anything, I would suggest that some bluer bulbs like 14,000K pheonix and 20,000Ks which can sometimes get monochromatic looking need supplimentation... with 6500K bulbs!!! From the corals POV, this scenario would be more relevant than supplimenting 10,000Ks with blue or actinic bulbs. But as it turns out, the PAR is the most important characteristic. Sure, some corals might pigment up more under one spectrum more than another, or have more red, green, or other spectrum needs... but with most halides, these bases are covered, as even in the bluest of bulbs, there is still some red, orange, yellow, etc.
Now, with T5s, the outputs can get more narrow. You could have a tank that is mostly blue and need to add some 3000K bulbs to bring up the red, as the blue+ type bulbs may put out loads of actinic, blue, and some green, and then drop off with no warmer spectrum output. In this case, a daylight bulb is needed.
With LEDs, its even more important to have good bulb husbandry, as these bulbs are 420nm, 450nm blue, 300nmUV, green, red, daylight (and these superwhites are still mostly blue)... so what you are saying with spectrum being more important will more likely ring true with LEDs in the future. But for 90% or more of what people are using right now, all the bases on spectrum output are covered, and the real only concern is how it looks to you, and PAR.
FWIW, the Red Tide / USB 650 spectrometer wasnt that much. I just find the PAR meter much more informative. The spectrometer is good for bulb comparisons, and getting info on certain bulb mixes/combos... but after that, its pretty much a one trick pony... you know what you are working with. The PAR meter, OTOH, will never run out of uses.