Well, I disagree. "Worst imaginable"? Those guidebooks are in their 7th and 8th editions I think, so obviously they're doing something right. Those guidebooks were responsible, for better or worse, for opening up much of the Colorado Plateau and West Desert to a generation of Utahns and others who grew up on them. Did they contains some errors? Sure. Maps are vague? Sure. Fast hiking times? Absolutely. But because of all of that those of us that relied on them in the late 80s and early 90s to discover our backyard Colorado Plateau were both inspired to go see these places while at the same time allowed to learn how to find these places on our own, without the overly detailed step by step instructions, gpx files, and the rest that so many mindlessly rely on these days. Sure, I use modern mapping tools, too, and I love a good gpx file, but I'm glad I, and so many others, learned to explore the canyons without perfect information to each and every petroglyph panel, campsite, etc. as we were able to discover the canyons on our own terms, which I think was one of Kelsey's original goals.
I see you making two different points here, so for the sake of not conflating the two, let's address them separately:
1) The Kelsey guidebooks aren't bad at guiding you.
This is a really tough position to take when you've already conceded that times are unrealistic, information is wrong, and descriptions are vague - ya know, the constituent elements of what it means to be guided. If you are going to use a Kelsey guidebook, you really must take into account that his voice is that of the (at least somewhat) unreliable narrator. Steve Allen's books don't have this problem. Nancy Pallister's book doesn't have this problem. Heck, even the Falcon Guides don't have this problem. It's a Kelsey problem. Doesn't his guidebooks aren't useful (see #2 below), but they are bad at their primary purpose of guiding you.
2) Kelsey guidebooks have utility above and beyond guiding you - as methods for idea generation and as a springboard for developing your own skills.
Agreed 100%, hence my comment about using Kelsey as an inspiration for further planning. Also, hence
the guide I wrote last year for a long-distance hiking route that I stitched together. In it, I warn prospective hikers that the data book is "skeletal" at best, and that potential hikers of the route must be comfortable navigating in the absence of complete or correct information. To be frank, my guide is Kelsey-like -
on purpose, because I don't want to destroy the pioneering spirit of the route with too much information and and a full GPS track, yadda yadda. If Kelsey showed any of this self-awareness and caveated his descriptions accordingly, I think that'd go a long way toward making his guidebook more effective.
TL;DR
@seekinglost - caveat emptor on Kelsey. Useful, but you must heavily supplement with other sources and accept the fact the fact that sometimes he's just dead wrong about whether something "goes". Bring an extra day of food.
Just treat it as there’s a good chance it goes somewhere in the vicinity and figure it out on your own.
