I'm of the right age that I had the Technical Manual in around 1977 when I was about 13-14 and it was just about the only thing available for any Trek fan. So needless to say, it's pretty foundational to my view and understanding of Trek. I know it's not canon by any means, but it's the source of many of the ideas that I'd held for a decade before TNG came out, and so I always give it the respect it deserves for the influence it had on my appreciation of Trek.
It also doesn't hurt that I played a lot of SFB in the 90's, which drew heavily on the Technical Manual.
Even with its inaccuracies, I'll always have a soft spot for it because of how important it was to my development. It helped fuel my love of Trek.