Valks in melee combat? I think it's entirely plausible. With how tough VFs are supposed to be, I've always kinda wondered why they seemed to never close with the enemy and grapple...especially when it came to battlepods. though we do see a fair amount of hand to hand in plus and frontier. Hell, the VF-25 enven carries aoversized combat knife standard issue.
On the subject of beam sabers and the like... yeah, lets not. One of my favorite things about Valks is that they are, for the most part, grounded in reality. Introduce laser oriented close combat weapons and not only have you made it too Gundam, you've made it too unbelievable. I see nothing wrong with a Sword with a PPB field, provided it will fit on the plane.
Of course, these are Your designs. Half of the fun of such an endeavor is throwing beleivablity out the window.