Oooohh!
Highlight a guide. I'm not sure if that would be referred to as "selecting" the guide? But definitely "highlighting". Yes, even for people who have excellent mouse manipulation skills, highlighting a guide requires....almost the most fine motor control of any Inkscape feature, in my opinion. I think that many able bodied, or able fingered people find that frustrating.
There are a couple of settings in Inkscape Preferences > Mouse, where you can set the grab sensitivity, and the click/drag sensitivity. I actually have my grab sensitivity set at 10! But I don't think that affects highlighting or grabbing a guide. I'm not sure why grabbing a guide should be any different from grabbing a node or an object. But even set at 10, I have to be right on top of the guide to grab it.
There are also several options for the mouse that you can set for your whole system. I couldn't offer instructions, because I only know about my mouse. But for example, I can set the speed at which it moves across the screen, set certain mouse gestures, and some other things. I have 4 mouse buttons, and 5 zones on the touchpad, all of which can be set individually. So for example, one of the zones I have set to maximize windows, another to minimize. I have my extra button set to do a double-click, because I find it difficult to double-click. But I can also set the double-click speed if I wanted to. I really find all these extra abilities quite helpful.
And I think in some cases, people with disabilities can use alternative input devices (mouses). For goodness sakes, if I were to set about to create the worst possible ergonomic mouse for myself, it would be the traditional mouse! I use a touchpad mouse and love it. And it entirely depends on personal preference or ability, as to which type of mouse is best. But there are several different types. I think a trackball mouse might be a good solution for many people with disabilities.
And after saying all that, I agree that it would be nice to have some kind of keyboard control of the guides. Or at least have the grab sensitivity affect grabbing guides
