added a comment - - edited
so some clarifications on various aspects of the .less issue, it's a bit disjointed as there are various overlapping concerns:
The 3rd party Bootstrap CSS is included unchanged. If you downloaded the bootstrap.css and bootstrap-responsive.css files directly from Bootstrap then you'd find the exact same CSS in the file currently called bootstrap.css (possibly changing that name to generated.css might be an idea). If you cut and paste the HTML of various bootstrap examples into a Moodle course they should all just work. But...
There is however some extra CSS before it, which is mostly a tidied up version of the CSS found in Moodle's Base theme changed to re-use variables like textError or textSuccess instead of various shades of red and green that it previously contained and some extra CSS after it, which is repeating some of the Bootstrap CSS in order to assign it to the ids and classnames currently found in Moodle.
The fact that the Bootstrap CSS is generated from .less files (also imported and unchanged from the upstream project) isn't massively taken advantage of in the current theme, the main thing is it allows you to easily apply Bootstrap styles to existing Moodle HTML. But it does mean that someone wanting to make small changes to the theme, like changing the color of links, or fonts can do so simply by specifying some variables e.g. "wellBackground" for the background color of "wells" (pale gray boxes used for blocks and some other similar areas). Bas has some Bootswatch-based themes on his demo site that show the power of this.
Applying CSS coding standards to generated CSS doesn't really make any sense. It's the exact same process as the concatenation and minification of JS and CSS that is already in Moodle. The stuff that gets worked on needs to look one way (optimised for people working on it and making changes) and the stuff delivered to the browser needs to look another way (as small as possible) to not cause unnecessary delays to users. This is also why it's just one CSS output file, but many input .less files. They're two different purposes with different requirements.
In fact, this is actually an improvement from the current situation for themers. If you go and look at the CSS in say the Base theme you'll see that parts of it are semi-minified, even though it's the form that people need to work on. One of the first things I did in order to work on it was to reformat it so that it was readable. The next thing was to break up giant files of unrelated styles into coherent groups, and then combine styles that were scattered in various unrelated places.
If you want to use Bootstrap as a base theme and make small changes that layer on top of it, then you can just use CSS and the current Moodle theme inheritance system. If you want to make more sweeping changes then you will be very, very pleased after you learn what you can do with less and how much time and effort it will save you. But if you don't want to learn less and you already know CSS then it's 99% the same anyway and your skills will transfer easily for small changes. Go and have a look at the files in less/moodle to see what you think.
Recess actually is a CSS linter, as well as a minifier and less compiler. Unfortunately in it's linting mode it complains loudly about the CSS that is required to work with current Moodle HTML (e.g. the use of IDs) so it's not very helpful at the moment as actionable suggestions are mostly lost in the noise.
Finally, are those CSS guidelines actually official? I agree with most of them, and follow them as far as possible with current Moodle HTML in the .less files but core Moodle CSS doesn't seem to follow many of them and the HTML (which is naturally linked) even less so. As I say, I think they're a good idea, I just wouldn't want to see them used to hold back improvements and progress in this area, as I'd imagine that's the opposite of what they were intended to achieve.
Actually, one more thing: Mary, where did you get that CSS file that you attached to the bug? I don't think that's from the Bootstrap theme.
Sorry, one last edit: If, for whatever reason, it was decided that unminified CSS, that follows Moodle's CSS guidelines, was required then it's an incredibly easy change to make. That file would be picked up and minimized by the inbuilt Moodle system (perhaps not as well, but probably not to any great difference). But... it's not the way it is by accident. It's not an oversight or mistake or laziness, it's a design decision about how best to take themeing in Moodle forward, given the constraints of current Moodle code and processes and the time pressure of a 2.5 release. I'd rather not change it, but I thought I'd make it clear that if we had to, then we could, very easily. I'd much rather people looked at the file, found it was minified and thought "What's going on here? Where is the file I'm supposed to edit?" and then found the right way to do it, rather than assume that things are the same as they are used to based on previous experience with Moodle themes because they find a nicely formatted CSS file in the usual place. As I said earlier, it's a message, a form of documentation, a way to guide people in the right direction.