Re: bugs in Luke that result in missing terms - I recently fixed one such bug, and indeed it was located in the DocReconstructor - if you are aware of others then please report them using the Luke issue tracker.
I just pulled down the most recent Luke code, and it does looks like that recent fix was made to cover the bug I saw. Unfortunately, the fix results in a null ref for me on my index. I'll open an issue, as it looks like all that's needed is an extra null check.
Re: Document reconstruction is a very IO-intensive operation, so I would advise against using it on a production system, and also it produces inexact results (because analysis is usually a lossy operation).
I hear you about it being IO-intensive. There's also other admin tools in Solr which do similarly intensive operations (the schema browser, for example, which generates a list of all fields and a distribution of terms within those fields). The intent of the tool is for one-off debugging, not for any kind of automated querying, but I'll try do some tests to see to what degree this tool is affecting our current production systems (I have not see any noticeable effect thus far).
Also, regarding the process being lossy. In this case, that is kind of the point of the tool (in my use) - to see what has actually been put into the index vs what was in the document sent to the engine. For example, if I index a field with the text "Wi-fi hotspots are a life-saver" with payloads on parts of speech, as well as stemming I want to be able to see something like:
"wi  / fi  | wifi  / hotspot  / are  / a  / life  / saver  | lifesaver "
With no payloads, this would simply be
"wi / fi | wifi / hotspots | hotspot / are / a / life / saver | lifesaver"
So I had initially named to tool the Solr Document Reconstructor, after the name you gave to the tool in Luke. Based on your comments, I think it might be less confusing for me to call it something like "Document Inspector", since it is not truly reconstructing the original document.
I'll try to get what I have pushed up today so you can check it out if you want. Thanks for your great work on that tool!