I have 04 TZ 3.4, its great and never felt it under powered, it gives me 5.5 km/l in city with AC. However, I think the newer the better. You have more accessories and stuff available and obviously will be in better condition overall.
Though, I have never driven a 2.8L Prado, but I don't think 2.8 will feel under powered, it really depends on the purpose you are going to use it for. For non-racing, city family drive 2.8L will be fine and will give you better fuel average.
Once bought, you will find that you will hardly use those bells and whistles of TZ or TZG. Furthermore, the more accessories, the more they are prone to going bad, if not maintained well. Specially height control uses air shocks and if it goes bad or its sensors, it may be a very expensive repair. It is not very much required for normal drive. It will only lift or lower the back of the vehicle by 2-3 inches and will automatically get back to normal when the vehicle reaches certain speed, like 40km/h.
