Should I trade my E70 or not?

[bmwx52008ba]

Hi guys, I live in Argentina and I own an 2008 X5 3.0si, with 84.000 miles.
I was considering trading my SAV in for a 2012 X35i.
Thing is, a new one here in Argentina sells for 110.000 u$s plus some extras.
When I bought mine four years ago, I paid 96.000 for it.
I looked at 3 BMW dealers, and the three of them agree on a valuation of mine of about 55.000 dollars, more or less.
I'd like to trade my ride, but losing 50% of its value in 4 years seems a little too much.
Their argument is that my truck has too many miles on, which I don't agree, but that's what they all say. The truck is in good condition.
I know the price of the same vehicle is about the half in the US, but is it normal that you lose 50% of the value within 4 years of use and 84K miles?
What should I do? The truck runs perfectly, but if I keep it, it would be even harder to sell it.
Or should I use it until it shows its aging and sell it for a lot less?