I got my '12 manual MK6 in april of '13 with 15k miles. Drove it bone stock besides cosmetic mods till last month, with 46k miles. I've driven my manual MK7 SE w/ LP 800 miles in 2 weeks. I absolutely love this car.
Performance kudos:
-better gas mileage on the highway, slightly less around town (in my experience)
-1st gear is much easier to deal with than the MK6's (mk7= tall gears, mk6= way too short)
-clutch is much grabbier than mk6 (same part # as the Golf R's clutch which comes with 292 hp/280 tq, compared to 210/258)
-no wheel spin even on stock tires
-negligible torque steer
-smoother, more luxurious suspension, yet handles better
-XDS+ set to strong narrows the gap between the non-PP/PP equipped cars
-2.25 turns lock to lock on the steering wheel becomes a luxury you won't want to live without quickly
-(entirely opinion-based) having driven both the MK6 and the MK7, I feel as though the MK7 truly embodies the qualities you think of when you hear the term "german engineering"
Exterior/Interior kudos:
-interior is just as nice as the MK6, just missing that Dynaudio system :\
-LED foglights go so well with the LP headlights, just need a Euroswitch (plug and play!) to run them with your LED DRLs
-bigger sunroof is very nice, only complaint is the tilt function is a little sad (tilts about 1 inch, whereas the mk6's was probably ~2.5-3)
-ambient lighting on the door sills and in the door inserts is SO NICE
-all interior lights are bright white LEDs instead of the yellow ones
-more room in the trunk than mk6
I could definitely say some more things, and would gladly answer any specific questions you have, but I think you get my point that the MK7 is a huge improvement over the MK6. Like many have said before, the MK6 was more of an MK5.5. The MK7 is truly a revolutionary step, as opposed to the MK6's evolutionary step.