@fayewatson 
some great ideas here, thanks for sharing these, I can appreciate the time and effort put into these.
Each point is all so useful. But just thought I’d my 2 cents.
1 - Building expressions where numbers or geographical addresses are the expected results and not being able to search is quite a time killer, especially with big pages. It would certainly speed up development, make things more fluid then having to scroll through lists of elements to find.
4 - Its quite a small thing, but very handy and just adds the extra layer of organisation.
5 - Quickly adding all fields of a thing into a workflow action e.g. create, make changes…would be another nice speed booster for development.
9 - Being able to multi-select elements from the elements tree would make things so much easier.
12 - This is quite essential, as is the responsive preview is pretty cumbersome, but having the data type render actually data would be oh so nice.
13 - Map extraction data like the custom dates composer is a great idea, will save having 4, 5+ expressions, consolidated into 1.
17 - Another useful time saver.
18 - This can get very tiresome having to create new gaps/spaces in between groups and elements. It would save having to use the empty hidden collapsing group trick and then fiddling around with getting the margins just how they were.
Just to sneakily add in a quick couple of ideas of my own into the mix 
- Real time pixel distances displayed when moving element & using ‘Show distance on hover’ in Design editor
- Allow one workflow action to set multiple page states at once.
- Allow a conditional property on a repeating group to change its ‘layout style’