Thanks for the kind words and for your question.
I'm on the road and working from memory, so bear with me. First, with regard to tags, I have had a number of requests for enhancing the Media Manager Modal Window (insert media). I'm working through what to do in this area. In the current MLA version you can select the taxonomy for the "filter by" dropdown in the Media Manager toolbar; maybe that will help. Go to the Settings/Media Library Assistant General tab and scroll down to Taxonomy Support. Check the box for tags (or Att. Tags or whatever) and also the radio button in the Filter column. That taxonomy will fill the dropdown and you can filter on that.
Second, bulk editing of caption and description isn't included because copying an identical value for the caption of many items doesn't seem of much use. What kinds of content are you thinking about for these fields?
Although bulk edit isn't available, you can use the IPTC/EXIF mapping features to load these fields from a variety of sources. Go to the Settings/Media Library Assistant IPTC/EXIF tab and have a look. In fact, with the Content Template facility you can compose caption and description values from a wide range of sources, not just IPTC/EXIF values. You can use literals, custom fields, taxonomy terms, etc. by entering a template in the "EXIF" text box. That might be a good substitute for your application.
Let me know how these features work for you and if you have any problems or further questions about them. Thanks again for your interest in the plugin.