>Beyond not losing concentration if I cast blindness on an
>opponent will having the spell at 50% or 100% effect the
>likelihood it succeeds? Will it effect the duration of the
>resulting malediction?

No and no.

>The players answering on the newbie channel were very much
>convinced the % of the ability has no such effect. It only
>qualifies the user for edges to learn a spell, or reveals
>knowledge of a resulting ability (assassin kicks, invokers
>etc) However even if this is true in most cases, I believe
>there are exceptions to this concept. Haven % learned as an
>example effecting the duration of Sanctuary.
>
>Are there other such circumstances even if in general this is
>not the case?

Yes; for example, sometimes having later spells in an invoker path gives a bonus to earlier spells in the same path. E.g. having Earthshield at 100 might give a bonus to Avalanche damage. Most other examples are called out in relevant helpfiles.