How do your kids like the foam? Will you be able to stick to foam builds in the future? It seems to be quicker and cheaper.
My kids think they are great. The foam torsos allow them to have more mobility. Last year they couldn't run with their Master Chiefs. The foam is definitely lighter, but I wouldn't say easier.
With pepakura, you already have the shape and measurement. You just need to cut and glue. With foam it is entirely different. It is like making a complex jacket where every pieces have to be custom cut and tailored. The gluing part is easy. I think the painting should be easy too - PlasticDip and paint.
Two disadvantages that I know of: the scale of the foam and the price. I'm using EVA foam that I bought from KMart, which is about 3/4 inch thick. I bought a 4 sheets/pack for $20. There are other thickness EVA foam that you can buy online, but they are not cheap at all.
I can say that foam has a lot of potential if the price of foam is cheap.