@fouad,
Im not exactly a cultus fan (but thankful to ALLAH for what he has given me), just got it this may and drove it for two weeks before i had to go overseas. Any ways i will try addressing your questions:
1)Engine performance is satisfactory and much better (especially compared to the old engine, no more knocking sounds). Though you are going to notice a huge difference after downgrading from a VTI. The A/C is pretty good, only problem i faced was that the timing came retarded from the factory (i too have the petrol only varient) so it had to be advanced (result was very poor pickup initially). So beware in case you face that problem.
2)Build quality: Nothing to write home about nor impressive. Some members have reported actual reduction in quality including plastics when compared to previously built vehicles. Seems PAK SUZUKI is indulging in severe cost cutting to improve profitability and beat rising costs of production. Comparing it to a City 2005 idsi, the interior and plastic used in the cultus is pretty shady.
3) Ride comfort: I feel that perhaps the newer model has better comfortable seats, besides the ride quality is pretty okay besides being adequate in spacing. Im a big guy 6"2 and i find no trouble driving the vehicle.
Lastly, as a piece of brotherly advice, PLEASE DO NOT SELL your VTI. Cars are becoming much much more expensive and shall be even more difficult than ever finding a good car such as you do besides people will be asking for insane prices. I feel a HUGE/MASSIVE difference when driving/owning it after a city 2005, let alone a VTI!. Any ways its your choice and wish you the best of luck with your new cultus, hopefully there are no unpleasant suprises waiting for you