Retitling this ticket to keep it more focussed as a generic "improve X" is hard to actually resolve definitely. I suppose the main goal here is:

* It should be easier to add the Nth parameter after having added one already (e.g. not having to go back to the template page from the navigation sidebar and adding a new one).

* One should be able to see other parameters (including their values) at a glance.

I've been thinking about the following UI changes (in no particular order, some options are mutually exclusive):

* Though having sidebar entries for each parameter (as opposed to just the template) is a nice way to jump to a specific parameter at once, but for other purposes it is imho too big and unhelpful. I can't justify its prominence other than that this is the only method we have in the UI right now to allow navigation to other pages in the dialog.

* I'd like to try for a Template to be a single page in the dialog where one can scroll from one parameter to another (e.g. more like a regular form).

* The sidebar should probably be reduced (parameters either not in there, or significantly less prominent (e.g. a third of the height and indented from the parent item). The navigation sub-items for parameters wouldn't be for separate pages in the dialog, but would trigger a scroll to the param section and (if not already) to go to that template page the parameter section is inside of. We could go fancy and update the sidebar in two-directions (e.g. clicking an item will scroll there, and if you scroll there manually, we update the sidebar active item.  This principle is quite common on one-page sites, example implementation of such principle: 
http://webdesign.tutsplus.com/tutorials/javascript-tutorials/create-a-sticky-navigation-header-using-jquery-waypoints/
https://webdesigntutsplus.s3.amazonaws.com/tuts/313_waypoints/demo/index.html

* As for bigger templates the "Template" page would now be very long, it becomes important that our "Add parameter" button is not only on top or bottom of the Template page, but accessible at all times (e.g. sticky on the bottom, and when clicked we attach a new section, add it to the list and scroll to it).

* Separate: I'd like to get rid of the [+] -> [+ {template}] button we have right now. It is quite counter intuitive in my opinion. Aside from the "+" being unclickable (one has to hover it, then find out there are different options and pick one, even though there was only 1 option, now there are 2: template and content), it is also too small. I'd recommend we either have both + buttons visible at all times (+template, +content) or put them in the sidebar are sticky bottom-positioned slugs/placeholders (e.g. each + item would be its own row in the sidebar, clicking it will add an entry to the sidebar).

</brain dump>