I agree that a GTI is a great car and I'm sure that's what I'll choose when the time comes, but I don't think it's a no brainer to do it now. My Golf TDI is amazing. I have 152,000 miles on mine. I upgraded to the CP3 pump, so that worry is over. And my car was loaded in 2010, with the RNS-510 and Dynaudio sound, so I'm not suffering with second-rate sound or functionality. I know the newest tech is a bit quicker and the backup camera would be nice, but you have to add a lot of cash to get into a new GTI. Mine would have to be an Autobahn. Then that car depreciates in a hurry.
For me, keeping the car seemed like a much better way to go. My Golf is just too good to give it up just yet! But one of these days, a GTI will be the replacement. It will likely be an MK8 or even an MK9! For those of you that already made the switch, at the time when I start seriously looking at a new GTI, I wonder if you'll be looking at a new car too.
Good luck with your new GTIs!