I do collapse individual topics from time to time. I do it for long ones in the default "all topics expanded" mode, or for any topics I just read when looking at the board in "all topics collapsed" mode.
However, I don't like the "click on the title to collapse" interface. In particular, I find it very much annoying that topics get collapsed every time I try to select (part of) their title for copy/pasting. I would prefer a small active zone (e.g. a visual indication of the collapsed/expanded state to the left of the title, in the grey title box) on which to click to change the state, while the title itself can be selected normally.
This said, collapsing individual topics may become less useful once we'll have a real ToC...
In case we want a quick access to "edit title", then again (double) clicking on it would interfere with standard text selection functionality (double click typically selects a whole word). More fundamentally, I think that such a quick access would be marginally useful and bring more confusion. To me, "edit title" is a comparatively seldom action and may therefore stay in the "other actions" menu behind the dots triplet icon. If this action becomes accessible with just one (double) click, then new/occasional users may suddenly find themselves in an "edit title" mode without knowing how they went there. They may even not realise what they are doing and just start typing something!
In any case, thanks for having brought this topic forward. I'm curious to read other's opinions on the matter.