Basically, if I wear something (or get a twist of fate) that gives +1 to might abilities does that give me more of a bonus on any given ability than I would have for maxing it out?
Skills can go over their max, but only by two points. If you have +3 to might, your maxed skills will only be two over their max, not three.
Some of the skills will only go 1 over max. This includes the might harpoon spell.
The weapon skills that provide new moves will not go over max. Unlike other skills which provide an increasing bonus at each level, like increased greatsword damage, these skills provide a distinct bonus at each level, and there's nothing extra to add at level 4.
I don't get what you're asking but I'll try to answer your question.
In this instance, yes, it will give +1 to all might abilities that you currently and will have. If you're asking if it will go beyond the max level, then yes, its possible to go beyond the max level of a skill, I once had a 8/6 skill as a finesse/magic character.