I don't think edge-coloring is considered less interesting. (Of course I don't think so, as it's one of my areas of research...) But I do think many people consider edge-coloring problems to be somewhat harder than vertex-coloring problems. The late Mike Albertson once told me that he thought of studying vertex coloring as wandering around in a dark forest, then looking up and discovering a small clearing---progress! He thought of studying edge coloring as wandering around in a dark forest, then looking up and discovering he was in the same place he started.
As for Vizing's Theorem... yes, any graph's edges can be colored using $\Delta$ or $\Delta+1$ colors; graphs in the former category are Class 1 and in the latter category are Class 2. Given a generic graph, it's not easy to tell into which Class the graph falls...even with plenty of information about the graph (example: graph is cubic and genus 1).
So my answer to your question is that there's less research done on edge-coloring because it's slightly harder than vertex-coloring is.