What is the required VA rating of the transformer in this LTSpice power supply?
You don't want to know the VA of the transformer, at least not as a single figure.

The core details and your working flux level will give you the turns per volt and the core heating, which are more or less independent of current.

You want to know the load rms current, which gives you the copper heating. Modify your Spice simulation slightly to compute the average current squared when driving your rectifier.

If you multiply working voltage by rms current, then you get a VA figure, but it's less useful than the two figures that contribute to it.