OK, let me rephrase; shield skill above the requirement is nearly useless. With my +3 Knightly Heater shield, going from 4 skill to 7 skill allows my shield to survive exactly one more axe swing. Weapons without bonus vs. shield are unlikely to break it even with 4 skill. Even with 7 skill:
-People commonly swing around my block even if I am facing them directly (this is unaffected by shield skill)
-Blocks won't raise within a certain window after dropping block (this is unaffected by shield skill)
-Ranged weapons still go over/under/around/through my shield all the time (this is mostly unaffected by shield skill)
-The shield weighs me down a lot (this is unaffected by shield skill)
-I get crushed through almost every time (this is unaffected by shield skill)
-I get block stunned by anything heavier than ~3.5kg (this is unaffected by shield skill)
Those three skill points would be better spent almost anywhere:
Ironflesh-nets me 11% more hit points
Riding-I could ride a Rouncey
Weapon Master-Increase weapon damage by ~3% and speed by ~1% (fairly crappy, but still better than shield skill)
Power Throw-30% more throwing damage and/or the ability to throw Axes/Javs/etc
Shields don't suck, but the shield skill does.
I see what you mean. You are probably the shielder I respect the most in game (and I hate fighting you

) but I think you may be looking at this wrong.
I think some of the suggestions you put make real sense to add -- but shield skill is very good because it lets you use better shields. Just like having more than 3 riding doesn't make your rouncey much better....but having 5 will let you use a much better horse. (an aside, I think having more points in riding than required
does noticeably increase the mobility of the horse).
Having 5 or 6 shield skill lets you use shield that CAN take much more axe hits and help with enemies trying to hit around your shield (huscarl shield, steel shield). Also, the if you get up to 6 shield skill, my steel shield resists crush-through the majority of the time. It also consistently blocks Ballista shots at point blank range!
If you are using a +3 rouncey with 3 riding and don't see the point in getting any more points in riding its kind of the same as using a +3 knightly kite shield and complaining that having more than 4 shield skill is useless. There is better equipment available to you with more skill in that category.
I know the tier 4 shields are kind of what everyone uses because they are fast, but personally I don't notice any difference at all when using slower shields...so these stronker, wider, beefier shields are definitely viable.
In the end, I DO agree that shield skill should do a bit more for you...perhaps increased block speed or reduced weight. However, I think another good way to make shield skill more useful is to incrase shield variety once you get to difficulty 5 and 6 shields. If we make more awesome shields that you need more skill to use, it will make sense to take more points in shield as well.