I own both Triple and Quad and the differences in signature, technical ability, cables quality, control ergonomics more than justify the difference in cost to me.
To be blunt the average person who is just wanting a nice IEM would probably stop at the Triple and be satisfied. But anyone who has tried multiple higher end IEM's and has become a "regular" on Head-fi will notice and appreciate the Quad's improvements. Looking at your posts I suspect your firmly in the second category.
The quads are just phenomenal!