Little Things - a bunch of individually small things that I didn't feel like turning into an addon. Collectively, it's a ton of stuff though. For example it makes it so unestablished users can't have a homepage set (link spam), adds more help topics under the "Help" tab, gives the "Staff" option under Members tab (and removes member list), adds "Undelete Thread" under Thread Tools menu when you are looking at deleted thread, etc, etc... Lots of little things (like the name implies).
Attachments & Avatars - stores them the database (not file system), disallows animated avatars if your setup allows GIF avatars (via ImageMagick).
New Content Filter - Checks all URLs and images in a post to make sure they are valid and not a redirect (cuts down on affiliate links, and cookie stuffing attempts via images). Can also check for certain keywords in posts that send them to moderation.
No Hyperlink - Makes it so you can't post links if you are not an established user (link spam prevention basically).
Premium Member - Lots of internal things, like adds/removes premium member's Twitter accounts to a private Twitter list we have which feeds the social bar on our site (end result = premium members have their most recent tweets show in our social bar). Adds some stats to the Statistics charts in Admin area (for premium membership... duh.. heh)
Thread Bumping - Allows users to bump their thread without posting in it to put it at the top of the forum. Also hooked into our marketplace so users can use it to Relist unsold stuff.
Enhanced Search - XenForo's Elastic Search. My "Search" addon adds "Areas" tab to member profiles and makes a bunch of content types searchable (users, conversations & reports). Makes soft-deleted stuff searchable. Adds Elastic Search stats to admin area.
Warning - allow moderators to immediately expire warnings they recently gave (accidental warning basically). If a warning is given for something that has an open report, the report is automatically closed. Make some adjustments to how many points users need to be banned based on if they are new or not. Calculate ban expiration date when needed (so user knows when there ban will be lifted).
Virtual Forums - allows a single forum to be in more than one place in the node tree.
Shaun I suggest a conference with KAM seriously. Some of your stuff is essential core.
Like I've long thought that new users should not be able to post links in content or sig to prevent spam. Similarly New Content Filter.
I'd love to see user notes, virtual forum, watch forum become available.
About 70% of your list is essential functionality to me. It brings Xenforo (as a relatively new platform) near the functionality level of vbulletin 3/4, without adding bloat.
I really hope that this essential functionality will somehow be added to the XenForo core, because it makes a world of difference. Out of the box the jump from vbulletin to XenForo is problematic feature wise. Your added functionality solves a lot of it.
Searching conversations is critical. I also think (possibly as a larger discussion about XF search in general) that things like user profile comments and... basically anything that you as a user have permission to see... should be searchable.
How much work was involved in writing the extension?