I always matt varnish, and I can't imagine not doing it. And it's not just to protect the models from damage.
When I finish painting a batch of figures, they never look 'right'. Most of the colours are satiny or even glossy, and after the final tedious stage of touching up all the mistakes I've made, it still doesn't seem like they are finished products.
A successful coat of matt varnish though, and suddenly they look finished. All the various stages of glossiness are evened out and dulled down , and I feel I can finally see the colours. Often just before I varnish I don't feel like I've done a good job - they seem messy, full of mistakes, the colours aren't right, etc.... I spray them, leave them to dry for an hour, and come back.... and WHAM, all doubts are put aside - they look good!
So I can't imagine not varnishing, even if for whatever reason you aren't worried about damage.
And in regards to metallics, I really like how the matt varnish dulls them down - I don't want them all shiny. I don't know if you'd call the end finish on my metallics matt or satin, but it certainly looks good to my eyes.