Without speaking to the merits of a particular law, one way that we can judge the success of a state sponsored initiative as a model for the country is the degree to which it is independently adopted (i.e. copied) by other states. Presumably, if a state seeks to copy and bring in another state's law to govern it's own citizens, then a majority of the elected representatives in that state see the law as having been a success.
To that end, I think you have to say that the "laboratories of democracy" concept that Justice Brandeis spoke of is in itself a successful model for the country based on the sheer volume of examples that exist. Just in the 2012 elections we saw several states (Maryland, Washington and Maine) vote to adopt same sex marriage laws, presumably based on what their electorate saw as successes in other states around the country. Similarly, the last several election cycles have seen the pioneers of medical marijuana (California notably) spreading similar laws across the country. Washington and Colorado even taking it a step further and exploring recreational marijuana use in their states. Perhaps other states will see success in these laws in the future and adopt them for themselves, or potentially they will fizzle and be repealed or at least spread no further.
Without going into a laundry list of all the different examples, I also found a smattering of articles speaking to this same point on issues ranging from education, to immigration and union rights which you can look at below.
Wisconsin Collective Bargaining Limits
Arizona Immigration Reform
Florida Education Reform