I'm currently developing new features for tighter integration in the IDE itself:
The first one is a dedicated Structure View for all configuration files (struts-config.xml, tiles-defs.xml, validation.xml) using the standard Structure View toolwindow from IDEA (I personally don't like the way Struts Assistant does this - using yet another toolwindow cluttering your screen). Ofcourse it supports all standard features from IDEA you know and love (Quick Search, Sorting, ..). It's nearly done and will be available in the next version :-)
The second one will be a new Project View - just for your Struts needs :-) But I'm still struggling with that..
Oh yes, and there's some noticeable performance improvements, especially when using Tiles - thanks to the excellent profiler from www.yourkit.com. Unfortunately the new background highlightings still are quite slow in larger config files, we'll have to wait until http://www.jetbrains.net/jira/browse/IDEA-7128 gets resolved (don't forget to cast your vote!).
PS: a few hours later, Demetra Build #5231 is out and what should I say.. the performance problem with highlightings is gone!