Do you agree, or are there some known hardware/firmware settings on the X2 that are very clearly able to give the enduser a better experience than some pencil-neck thought to allow us without having that root access?
Yes, I agree. The X2 can't be overclocked (I believe it's due to having a locked bootloader, whole nother subject there) so that's a non-issue anyway. There are lots of neat and helpful apps that require root, but very few will actually help the phone beyond an interface-like level.
Once you move up to using a custom recovery (Bootstrap, in the case of the X2) you can start to change and improve how the phone functions, but the changes aren't massive. You'll hear people say "my phone runs so much faster/smoother/better," but to be honest the Droid X2 is
fast, regardless of whether you're 100% stock or completely customized (though you can bork up your phone if you overstep your reach).
Personally, I'm a big flashing junkie. I'm more interested in what I can get my phone do and ways to make things work than anything else. The single biggest argument I would put forth for not customizing your phone very much is that it takes time, effort, upkeep, and oftentimes patience to do it, and the more you do, the more it takes. If you're not interested in spending free time fiddling, downloading, backing up, flashing, fixing, etc. then just root your phone for the purposes you really need, and leave it at that. Maybe grab an app manager like Titanium Backup or AntTek App Manager to backup your apps and their data, or grab ROM Toolbox and try out some minor customization, stuff like that.
I've heard of poor still photo performance, is that an area that can be noticeably improved by alt drivers / apps that need root?
I've heard the same. I rarely use my phone as a camera though, and when I do, it's for simple things like something to throw up on Facebook. I'm not up on fixes or apps that improve quality. If it was an issue for me, I'd search here, xda, DroidForums, maybe RootzWiki for some things to try.