You have to watch out for settings such as "A Tale of Two Cities".
If you are going to do it for capitals, it's a good idea to substitute "space.caps" that is wider than the default space, in "calt", to improve the look of all-cap setting.

I don't think it really improves colour, and can be really nasty if a typographer uses H&Js that reduce wordspace.

Myriad has this feature, which is part of its really tight set. In general, it is very very slick, but it does fail occasionally, and it looks like the space hasn't been set, a typo.

Does creating a contextual space character work with InDesign? I had tried doing some contextual space work a while back and found it worked fine with Illustrator, but it seemed InDesign had its own space settings that override those programmed in the font.

Given the answers, I don’t know if I got what you mean, but I make something like this:

H | H
A | A
T | T
V | V

This way, I can compare /H space H/ against problematic letters.

Be very careful about kerning lowercase letters against the space. I’ve seen books where the pair was too tight and the space just disappeared any time a line was tight.

You also need to think not just in terms of pairs, but triplets. Consider kerning "space" "W". Now consider what happens if a lower-case "f" precedes the space, as in "If Westmoreland had only . . ."

I just rekerned a font where, amongst other things, the comma-quoteright kerning was so tight that the string f+comma+quoteright had the quote overprinting the terminal of the "f". Or another font where A+quoteright+comma was kerned so much that the comma overprinted the right arm of the "A". I know, none of these involve spaces; the point is to think in terms of the effect of pairs kerning in three+ letter situations.

The deeper into a wood, the more trees I see. Thank you - I can see I must be more careful than I thought.