I was asked for lots of usability improvements like this. Usability is important though I felt them pains in ass some time as I was the only UI developer for tons of views, tons of back-end testing, and no any help from designers, also pushed by unknown deadlines. I made complex validations which follow-up almost every user interaction, even when editing itemRenderer in datagrid, compares changes. The result is nice and I like it, though it cost time, and I felt I could never have an end to a perfect production(changes more frequently than improvements), and not easy to maintain and change, at least more testing hours.

My own opinion in this case, I would first to finish big things like functionality and main interaction design, then go through usability and improve details all together. That will be much clear and organized in mind, make solid progress even use less weeks, and get real quality control.