Plant anatomy is an old field, so should today's systematists be interested in it? Yes, most of them should, to some extent. For their own selfish reasons. Having knowledge of plant anatomy, being able to make sections, being able to use an electron microscope, and being able to teach a plant anatomy course are all skills that the employer of a systematist might find very attractive. Remember that your employability depends on your having skills that a particular employer wants--so if you have skills in structural botany, you as a systematist look more interesting to many employers than systematists who know little about plant anatomy.
Plant anatomy is still a vital field in which knowledge is synthesized. Phylogenetic trees offer hypotheses about divergences of taxa, but plant anatomy can offer underlying reasons for those divergences. Plants present structures to the environment--most of the tools that a plant uses for survival can be described in terms of anatomical structures. Consequently, plant evolution is, to no small extent, the story of changes in structures so as to suit environmental conditions. So there's a rich dimension awaiting you in plant anatomy.
Sherwin Carlquist, Santa Barbara