The choice is up to you, every car/engine has it's pros and cons.
You could buy a VZ that has been looked after really well and serviced regularly and it will be a great car (same with getting a VY), or it could have been thrashed or neglected, oil not changed regularly, overheated and it could start costing you.
Yes the Alloytecs can have their problems (or not), but I know a guy who had a VX Wagon with the Ecotec, he overheated it and ended up blowing the head gaskets, so we replaced them, then 12 months later he done the same thing but this time he stuffed the engine.
Common problems with Ecotecs are the sump gaskets leak, rear main seal leaks, rocker cover gaskets leak, valley cover gaskets leak, engine mounts wear out fairly quick, supply hose from power steering reservoir to pump leaks, anything can happen and it doesn't matter how good you look after it.
Yesterday we had a 2007 VZ Wagon Alloytec come in to work with 60,000kms on the clock, had a miss in the engine and turned out one of the coils was faulty. Proves the point of you can look after a car and something will still stuff up.