Are there restrictions on CAS entry? Would a VLA be classed as a microlight for those airports/airfields which don't allow microlights?
None of any real significance - class A is closed to most of us and that doesn't change, and you need a radio for most CAS penetration and that doesn't change.
A VLA wouldn't be classed as a microlight anywhere that I'm aware of.
And finally for now... does a PtF still require a periodic certification check to revalidate the Permit? And if so, is this as 'strict' as a CoA or something much simpler?
An annual inspection and check-flight, taking typically half a day to a day - much simpler and cheaper than a CofA renewal. For a CofA renewal it's basically a strip-down inspection with the licenced engineer (or maintenance organisation) taking responsibility for the airworthiness of the aircraft. For a permit renewal, it's essentially an audit of the owner's good care and maintenance of the aeroplane, so the owner continues to have primary responsibility.
Is there any clear statically proven safety benefit to flying a CofA machine over a Permit machine?
My stats are a bit out of date, but circa 2001...
PtF light aeroplanes: 1 fatal per 33,000 hrs
Microlights: 1 fatal per 50,000 hrs
CofA light aeroplanes: 1 fatal per 70,000 hrs
(Gliders and light helicopters are about the same as microlights). Offering an opinion, I think that the differences here are almost entirely down to differences in the way the classes are operated, and not the basic safety of the various aircraft. For example, PtF light aeroplanes tend to be more operated from "solo" strips, microlights from clubs where there's a lot of safety support, and CofA aeroplanes spend most of their time around flying club environments which are quite strictly regulated by the local CFI. [This is however purely opinion!]
G