Don't make 'readonly' fields less readable
secretgeek.net
secretgeek.net
The key is to make it not look like an edit box, then people won't think they can interact with it. You can see it in practice here at HN: edit a submission and you can see that the URL is not in a text-box, so the text can appear like any other text on the page.
In general, making things harder to read can't be good, and should never become a standard.
It reminds me of comments here on HN which have very low scores: they get greyed out and effectively "disabled", like a disabled form field.
However, disabled form fields which demand no interaction, not even reading, from the user should not attract interest. It's fine to make fields which are unimportant less prominent.
As you say, real read-only content (such as the text on a web page) should both be easy to read, and not shown inside a user input control in the first place.
This would be an argument to not show them at all. Requires no interaction, conveys no information and doesn't attract interest? Then it is only cluttering your UI, consider removing it.