That's a wonderful theory, with two problems:
1. If this law managed to accomplish its main intent without all the collateral, it would still be bad law, but it would no longer affect the mayor's kid and the senators wife, much less the businessman selling nail guns. Moreover, those groups could easily have the law reformed to still achieve its intended effect while no longer affecting them. (Guns are evil and scary, doncha know.) In either event I would continue to argue that less enforcement must always be better than more.
Again, if the gun law applies to everyone it is more likely to be repealed than if it is enforced only against an unpopular minority. Enforcing against a small minority is offensive and might go on forever whereas if enforced against everyone, there is greater chance of a demand to repeal.
To a different topic, if rich white kids got treated exactly as poor black kids for illegal drug use and possession, how long do you really think it would take for rich white parents to demand some changes in the law? I note that with a black president and black AG, the DoJ is very actively making changes in sentencing guidelines for various non-violent drug offenses. Coincidence? Clinton admitted to trying a little dope as a kid. But did his children and grandchildren run the sake risk of having their entire lives destroyed by a minor offense as do those children who are likely to be personally known to Obama and Holder?
2. I see little evidence that your contention is actually true. Every Californian is, for instance, equally subject to the state's onerous yet silly firearms laws (no standard capacity magazines, handgun roster, AW ban, etc etc etc) yet these remain un-repealed.
First of all, rich Californians can obtain may-issue permits to defend themselves. Or the truly rich can hire private security and not even have the inconvenience of carrying guns themselves.
Secondly, it is entirely possible that the gun laws of the left coast are actually quite agreeable to the majority of their citizens. If that is true--and I see no evidence to the contrary considering who they elect as their senators--then the only recourse is to fundamental rights that must be protected against majority vote. The courts seem to be coming along slowly on that one for RKBA.
The best you can say about your approach is that it might eliminate laws above some certain degree of onerousness. Assuming the current law does, in fact, exceed that level, it would take remarkably little "reform" to rectify that whilst leaving a bad, immoral law on the books.
The approach might help to eliminate laws the majority finds more than some level of offensive. Obviously, if the majority finds the law agreeable, then by definition, only a minority is likely to suffer.
"Fixing" the law to apply only to firearms would make the law less offensive--though no less unconstitutional, IMO--than applying it to nail guns. And that could happen. But the point is, enforcement of the law would lead to some change in the law until the law is less offensive.
There is no guarantee of perfection.
For better or worse, in a constitutional democratic republic, we can get the government we deserve. The population of Washington State voted to create a really bad law. In the absence of evidence of vote fraud, this is what the majority wants. It is offensive to our rights. But it gets rather difficult to overcome majority sentiment in any system (like citizen initiatives) where majority desires are allowed to rule. Allowing minority sentiment to rule can be just as bad in many other cases.
Charles