EUREKA! I found it!

The way I achieved this marvelous setup, was with a combination of a tiny AppleScript saved as an .app file, and the brilliant, free third-party prefPane app, Do Something When.

Instructions:

Set up up the first part of the process as linked to in the question, which will give the following settings in AutoImporter (so that when you insert the iPhone, it will automatically import them to the Pictures folder):

Now go to Script Editor.app (/Applications/Utilities/Script Editor.app), and insert the following code, which is what will open the Pictures folder in Finder (replace yourosxuserdirectory with your own user folder name):

tell application "Finder"
    open ("/Users/yourosxuserdirectory/Pictures" as POSIX file)
end tell

Click Save or Export and select 'Application' as 'File Format' near the bottom. Save the app file (I named it openpicturesfolder.app) to somewhere on the system drive where it won't get disturbed later on or accidentally moved/deleted etc.

Download and install DSW, open it from the System Preferences window, and create a new rule, exactly like below ('openpicturesfolder' simlpy means the .app file that you browse for DSW to 'Open' when Autoimporter launches):

Click on Start up the top, tick Automatically Start on Login, and you are on your way to iPhone/camera photo importing bliss.

DONE.

I'd go for the 'not quite cave-man' approach - though still a bit manual...

• Launch Image Capture.

• Plug in iDevice

• Select any/all photos you wish to delete

• The Delete button is at the bottom of the window [the 'no-entry' sign]

After comments - the button is still there in Yosemite.

Update Nov 2015 - the button is still there in El Capitan, though it is now black & white, not red.

Picture updated to Image Capture 6.7 after further queries on the button not being there.

Update July 2016, as people are still missing this bit...

If the Delete button doesn't appear, eject & re-plug the phone.