Open Vim in Terminal (iTerm) from Finder - copied from http://thepugautomatic.com/2015/02/open-in-iterm-vim-from-finder/ and updated to open in the current terminal

TerminalVim.scpt

on run {input, parameters}
	set cmd to "vim -c startinsert"
	if input is not in {} then
		set myPath to POSIX path of input
		set cmd to "vim " & quote & myPath & quote
	end if
	
	tell application "iTerm"
		activate
		set myTerm to (current terminal)
		tell myTerm
			set mySession to (make new session at the end of sessions)
			tell mySession to exec command cmd
		end tell
	end tell
end run

Ok guys I took the challenge as well and here is my gist : https://gist.github.com/chaadow/5e8ed49c333008eec0c3ced07451ee48
It works for El Capitan.

It handles 2 scenarios basically :

• When Iterm is not open :
  • It doesn't create a second unnecessary window, since it knows that it's startup
  • It tells the current session to run vim with the appropriate POSIX path
• When iTerm is open :
  • If there are no windows open ( This is the case when you have closed all windows but iTerm is still open, kinda frequent for me)
    • It creates a window with the default profile
    • It runs the vim command
  • If there is at least one window open
    • It creates a new tab so that it doesn't override the current tab of the window
    • It runs the vim command

Even though the script feels repetitive, this is the only and simplest way I found to handle most of the edge cases.
Alternatively, according to the iterm documentation, there is a is at shell prompt option, that allows to know if the current session if "free", so we can run the vim command without the need of creating a new tab each time.
However it requires installing the shell integration utiliites inside of iTerm, and this is not a "simple solution".
Cheers.