I'm on my 2nd Up!, the first being a 2013 High Up! with all the toys on it. It now belongs to my son, which apart from a lack of power (75bhp and not a lot of torque!), he is quite happy with it. I had no major issues in the 5 years I owned it, and so far with my son, it's been good. It's now on 83k miles, I bought it in 2014 with 7500 miles on the clock.
My GTI is 5 years old in April, and sits on 73k as of today, and I love it. The remap has helped tbf, but despite the lack of illuminated switches, I don't have any major gripes with the car or how it performs. Side by side, the dimensions of the cars are identical, underneath they are pretty much the same too, so I don't really get all the hate they seem to be getting on this thread. As I've said before though, the Up is a great car, just not as 'special' as the Lupo, certainly in GTI form. The other Lupo I have access to is a 1.4S, and the Up compared to that is streets ahead, both in terms of equipment and dynamically. I guess on a Lupo forum though, there will be more love for the Lupo!