For digital plates, you really have three choices of laser types (and wavelength) based on the vendor and class of CTP you choose: 830nm (most thermal systems), 808nm (really only one major vendor of thermal systems), and 405nm (violet lasers). The plates themselves will be sensitive a bit above/below those frequencies, but the lasers are wavelength-specific.
<edit>PS plates ("conventional" plates exposed with film and a UV lamp) have a wider sensitivity anywhere from 320 to 450nm. UV lamps don't output just a single wavelength of light like a laser, but a broader spectrum in that general range. Violet plates fall into the same range of wavelength actually, but have to be MUCH more sensitive to exposure than conventional plates because violet lasers only have 5 to 120mW of power. (Thermal laser systems can deliver 100W of power or more to the plate) </edit>
Regarding developer usage: it's hard to give a global statement for all plate types because of the regional variations in products and practices, but for the latest digital plates (at least from Kodak) have far less developer use than older digital plates and essentially all conventional plates. Even if the cost per liter of developer may be a bit more, the total cost should be competitive or better. This is an area where we've made huge improvements even in the last 1-2 years.
Kevin.