I don't really understand what would the problem be on the highways. Why are people so obsessed on highway power? To begin with, speed limit would be 60 MPH or 100 km/hour on most roads and police won't arrest you for driving at 80 km/h or 55 MPH (just under the speed limit). This car has enough power to get to the speed (I own manual 1.0L and I only need 3rd gear to get to 100 km/h, if I push it I can get there on 2nd gear but no, bad for engine). Once you're at the highway, turn on cruise control and just cruise away?
If your drive to get the car is the economical driving (low fuel consumption) and low price, get this car. I have driven it 10k KM and yes sometimes I miss the instant power when you need to evade dangerous situations in the city. but I have never had any problem on highways (speed limit in Holland is 130 km/h and unlimited at some highways in Germany). If you want more power, sacrifice fuel consumption and get a 2.0L+ engine (I love my Galant).
Good luck with your choises, I love this car now, it's a small cute and marvellous to drive.
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View my fuel log 2013 Mirage 1.0 manual: 47.5 mpg (US) ... 20.2 km/L ... 5.0 L/100 km ... 57.0 mpg (Imp)