Circular Ward Against Demons (and others Rego Vim wards) needs to penetrate the demon might, and if not, why?
Yes, like all spells wards need to penetrate to have an effect. This makes wards weaker than the guidelines may suggest. In particular, it is often easier to kill a target than to ward against it.
I think changing how wards work is a fairly-common house rule. See for example the offers in the Big List of House Rules over at Project Redcap (link).
I've actually found wards quite powerful even though they do need to penetrate. The common argument against penetration is roughly that you might as well just strike the target if you have to penetrate. However, wards have two huge benefits. First, you can set them up ahead of time. Second, they work against an unlimited number of opponents. House ruling so they don't need to penetrate can make them way more powerful than people expect.
I agree with callen. House ruling they don't require penetration can make magi (and their companions) relatively immune to enemies with might they wouldn't otherwise be able to affect with their magic with just 4 spells and a semi-decent rego vim score. Which makes parma magica redundant against non-magi since a ward also blocks physical attacks.