Obviously this is a rather small subset of the books by him that I own; I think I have read more books by him than by any other writer.
The novelisations of past Doctor Who stories which I read before I was a teenager were hugely important in an age where TV existed to be watched once and then lost forever except in memory. But even more important was The Making of Doctor Who, the one and only book about the show, which for the first time made me realise that you can write about stories as well as writing stories. (I was 9.) It was an early part of the process that moved me from just being a reader to being a fan.
A lot of people have reflected on his personal kindness. There’s a collection of anecdotes published as a freebie by Candy Jar which you can download here, some of which are very moving, even the ones that are not all that personal.
My own Terrance Dicks story is brief but important to me. I met him only once. One afternoon in 1980 or 1981 (I remember his grimace at mention of the then recent Nightmare of Eden) my brother (aged 12) and I (aged 13 or 14) got wind that he was speaking in, of all places, Suffolk library, a mile or so from where we lived. I am pretty sure that it was the first time I had ever met a celebrity, let alone a Doctor Who celebrity. (Little did I know that my little cousin Brian, then aged two, would grow up to be the producer of the show.)
I don’t remember much about what he said (I asked why Nicholas Courtney wasn’t in The Android Invasion, he said that it was probably due to other acting commitments). But I do remember that he was very pleasant to and patient with a crowd of excited young Belfast fans, and set a standard of behaviour that I still expect from celebrities dealing with the public (or with me); and I deal with a lot more celebrities now than I would have ever expected back then.
A little kindness can go a long way, and Terrance Dicks showed a lot of people a lot of kindness in his life, and not only through his writing. An example to follow.