Are we obliged to sacrifice because we have bought a new car?
It is natural that human-beings thank Allah for the benefactions He bestowed. This thank can be a valid type of worship; however there is no condition that you should sacrifice because you bought a car. Sacrificing and delivering the meat from this sacrificial to thank Allah is a good deed. This becomes a sacrificial of praise. That person may perform additional (nafilah) prayers (salat) instead, which becomes a prayer of praise. None of these are obligatory, though.