I see them as doing different purposes. Vector etching is perfect when what you are dealing with is fine, precise lines. You can’t do broad areas or fills with vector etching. Raster etching treats everything as a fill, essentially. I wouldn’t trust raster etching to get the finest of lines or the most precise detail, even though it’s probably fine (I think raster etching is limited to 500dpi resolution, which is coarser than vector etching can theoretically give you).
Vector etching is decidedly faster for a few lines, since raster etching has to scan the entire raster area to etch. But the machine moves faster when rastering than when vectoring, so if you have a lot of fine detail vectoring can take longer. Raster speed depends only on the size of the image, not on the complexity of it.
I would say that Epilog designed the machine to do both, with the understanding that the machines would be used in a commercial production environment. Commercially, more rastering is done than vectoring, so that’s probably where the emphasis in machine longevity went into it. I wouldn’t personally consider machine longevity as a major factor in deciding how to do a particular job.
As for energy use… It’s probably a wash, with a slight benefit to the vector etch. To get similar results on the material, similar amounts of energy still have to be imparted to the target. Whether you do that slowly at low power, or fast at higher power probably doesn’t matter. The rapid speed of the gantry when rastering probably uses slightly more energy than the careful movements of vectoring, but it’s probably pretty small.