A quick look on Auto Trader tells me that both cars seem to be around the same value...
Personally I prefer the 180... but I would be pushing for some money your way, especially if your car is perfect and this 180 seems to have a few niggles...
I think its going to come down to condition of the 180 compared to your 160 and personal preference as to which you would prefer to run.
Remember if he approached you then you may have the ability to haggle a bit