Update provided Solr 4.x solrconfig.xml [#2428093]

While trying to configure apachesolr_attachments 7.x-1.x (stable:7.x-1.3 as of feb 2015) to remotely extract files from a Solr 4.10.2 I've discovered that the Solr-provided solrconfig.xml and the module-provided differ a lot. I imagine that the module-provided file has been made obsolete/outdated by later Solr releases.
For instance, for the above case, I've discovered that the module solrconfig.xml is broken if you want to use server-side extraction (separate issue), even after applying the solrconfig.tika.patch.
In this issue I'll try to keep track of differences/inconsistencies/bugs/doubts about the module Solr 4 provided config. Use this to discuss how the overall process can be improved or made easier. For instance, instead of keeping a full solrconfig.xml, we could keep a collection of patch files to apply on stock solrconfig.xml file, as it is done with Debian packaging, for example.
Apart from summarizing open/new issues related, it will serve as documentation for contributors not familiar with the module. There are some issues related with Solr configuration, especially with server-side extraction.
Issue queue recommendation: there is a 'solconfig.xml' tag. Add it to any issue you find related to this.
Notice: this issue is not meant for solrconfig.xml configuration support. File specific issues and link them here.
Added to this, you might find configuration issues valid for Apache Solr Search module filed in the Search API Solr issue queue, since both looks like that share a lot in terms of configuration. Same applies for both '_attachments' contrib modules.
There is even a sandbox project (Apache Solr Common Configurations) dealing with configurations, but quite low on the radar, IMHO.
Since this involves several modules, it might be desirable some knowledgeable feedback on this to point contributors in the right direction.

To recap:

Maintainers' approach and practices with config files
How can be solrconfig.xml maintaining be made easier?
How much should module's own solrconfig.xml should differ from stock?
Which differences are presently required for the module to work? (let's keep them doc'ed)
Add links to issues for specific configuration cases, e.g. server-side extraction
Improve/update docs

Related issues:

Perhaphs they can just be addressed with an updated solrconfig.xml or, at least, with a docs update. The handbooks do not have too much info about the configuration files.