The Highline gets airbags and abs
which are safety features. Further, the new highline will get stereo with usb/aux, steering controls, new alloys, anti pinch windows and most of the things that are desirable in a modern hatch.
For me, the features do not matter, but safety did. So, bought highline only for safety. In my opinion, you should go for Trendline version and do some modifications later like alloys, music system, some performance mods if possible.
Yes, 1.2 will score low on performance as compared to 1.6, but you should keep in mind that 1.6 would not be easy on pocket considering the cost of car itself while purchasing and further maintenance too. As far as I know, there have been no free AMCs for 1.6.
You will not be disappointed with 1.2. Its a sturdy, fun filled and solid car that's something to experience. Take a thorough test drive and decide. I am here to answer any of your query regarding polo petrol.