You don' t provide enough information on which to make this decision. You first have to know the goal, which from your post I'd assume is to bring the sex ratio and age structure of your herd to a more natural level, which almost everywhere means protecting younger bucks and killing more does. You then need to determine by sampling, which, in this case, antler characteristic, most reliably and practically accomplishes that goal.

sgara is most on target with his comments, in my book. A 3 point restriction in most of the US will result in removing the genetically superior antler growing animals from the 1 1/2 year olds in the herd. I doubt that's what you had in mind. Where I live in Maryland, this restriction would allow removal of 50% of our 1 1/2 year olds. At 4 points per antler, we would still lose 40% of the 1 1/2 year olds. A 5 points rule would protect almost all of the 1 1/2 year olds, but would be unaccepatable to hunters, as it would also protect 30% of the 2 1/2 year olds, including some seriously impressive animals.

The 13 inch spread requirement is better, but where I am in Maryland, would still dig into 15-20% of the 1 1/2 year olds. Here, at 14 inches, we would protect 95% of the yearlings.

As to enforceability, abiding by the game laws is almost entirely dependent upon the morals of the public. 90% of hunters will obey the rules, provided they believe game management decisions are being made in the best interest of the game and hunting in general. The would be some initial frustration with the spread rule, but studies under such rules in Georgia showed hunters were surprisingly good at it and the frustration subsided.

As for spikes, where I live, almost all spike bucks are the result of later birth dates of fawns, caused by the skewed sex ratio of the herd. They are not genetically inferior and could turn into large racked bucks. That said, removing a spike from the herd will have little impact on the future number of 3 1/2 and older bucks. This is because the probablity of a buck surviving is only around 60% each year. The spike is already a year behind the curve and is going to have to survive an extra year to catch up in antler growth to his cousinborn earlier in the same year. Only 1 in 5 bucks will make it to 3 1/2 and only 1 in 8 to 4 1/2. Bottom line, there's only a 12% chance you hurt your chances of seeing a good racked mature buck somewhere down the road by shooting the spike. Given you have to feed him during that time and that you probably already have too many deer in the herd, shooting a spike is not a lot different than removing a mature doe. That's my two cents.