Pat,
I'll give a contrary view. For birding I use zoom eyepieces almost exclusively (Zeiss, Swarovski and Nikon) because I don't want to keep up with extra eyepieces or take time to change them. The great advantage of zoom eyepieces is that they allow instant choice of the most useful magnification for the conditions. If the air is unsteady that may be 30x or less, but when the air is calm I've successfully used magnifications above 100X. To see all the detail available from a high quality 80mm scope requires at least 60X (really more like 70-80X), provided the air is steady enough. The best current zoom eyepieces have no optical disadvantages at high magnification compared to fixed eyepieces. They are just as bright and sharp. All the dimness and loss of detail come from the limitations of the telescope objective lens, not the eyepiece. The low magnification views through wide field eyepieces can be very impressive (I sometimes bring along my favorite such eyepiece, the 30X swarovski), but I would never want to be without the ability to take advantage of the scope's full resolution when the air is steady enough to allow it.
Henry