Speed limits are fine when they are set at a reasonable level, when they are not (and are enforced) then the law is an ass. And that applies if the limit is too high for a given road equally as for limits too low. Examples:
* The speed limit on the motorway system is 100km/h, same as for most of the open road. But you will be much safer driving at 100km/h on the Northern Motorway than (for example) the gravel roads going out towards Raglan. I competed at a Rallysprint on one of those gravel roads a fortnight and I only got above 100km/h twice. Ergo, IMO the speed limit should be lower on the gravel roads to recognise their relative lack of safety for Joe Average.
* The speed limit on Oteha Valley Rd (on Aucklands North Shore) is pegged at 60km/h. Along this 2km stretch of dual-lane road there are 2 roundabouts and no other sideroads/driveways. What you get is a dangerous situation where some people stick to the 60km/h speed limit, some people the de-facto limit (with tolerance) of 70km/h and others do 80-90km/h. And this is just mamma and pappa driving their everyday cars in everyday ways doing these speeds, not boy racers. So if a normally law-abiding citizen feels safe doing a speed higher than the marked limit is the limit in fact unreasonable?
Australia is interesting to drive in. Most drivers are of similar skill levels to NZ drivers but not all have the agressive attitudes we have. Their speed limits for urban roads are usually 60km/h (going up to 80km/h for more open stretches) and 50km/h in residential streets. Motorways and open roads are 100km/h or 110km/h. Their speed limits can vary quite frequently on a single stretch of road, depending on what each part of it is - Springvale Rd in Melbourne can change between 60km/h and 90km/h limits every 800m or so! But even as a visitor I usually find myself sitting on the correct speed limit by virtue of driving as quickly as I think the conditions allow. Funnily enough on urban roads in NZ doing the same thing I usually find myself almost exactly 10km/h over the marked limit.
Raising driver skill levels may help a little but having spent a number of years as a Prodrive tutor I know just how bad the driving skills are of the average citizen (not only learners, parents too). I think trying to educate NZ drivers to a decent standard would be akin to trying to shovel shit uphill with a pitchfork. And the most difficult part of the job would be changing the mental attitudes - you can train most people how to control a car but it is far harder to change their attitudes.
Another thought on urban speed limits; as far as I know the speed limit of 50km/h was drived from an original 30mph speed limit before metrification (correct me if I'm wrong). Surely a modern car is capable of stopping before and/or avoiding a sudden hazard than a car made in the 60's/70's when the speed limit was introduced? If so then why make people drive slower than they already do.
So in summary I don't mind if the speed limits get enforced more rigidly but ONLY if the speed limits are set at a reasonable level in the first place, and I don't believe most of our urban-road limits are. Driver education would help but I hold no hope of changing driver attitudes, which is the key.
Very lengthy rant finished