In practice, it's nothing like that. At least I can't imagine Rhode Island introducing a "RhodeCoin" on six months' notice.
Are American states suffocated by the federal structure? Maybe, but Estonia is also a member of the EU and the Euro currency, so clearly it doesn't have to be automatically like that. (My personal opinion is that the EU/Euro are actually much more innovation-friendly supranational structures than they're generally given credit for. Estonia's economic growth has much to do with their EU membership.)
In fact, both of your examples illustrate this. When gay marriage was only legal at the state level, same-sex legally married couples weren't treated as married for the purposes of income tax, Social Security, immigration, and a bunch of other federal benefits. And even in states where marijuana is decriminalized, the DEA can arrest and federally prosecute you if they feel like it.
For both gay marriage and marijuana legalization, for example, certain states tried it against a chorus of voices that said "This will lead to the destruction of marriage as we know it" or "crime will go through the roof". And then that didn't happen, and so other states tried it, and eventually it filters up to the federal level.
There have been other cases where policies have been tried that did lead to widespread chaos and negative consequences, like Nebraska's safe-haven law that defined a child as anyone under 18 and led to mother's abandoning their teenagers because they didn't want to deal with them, or California's Prop 8 that was supposed to keep senior citizens in their homes but had the unintended consequence of restricting the supply of housing and driving housing prices through the roof. In these cases, the laws have not been duplicated in other states, at least not without changing the problematic details.
There's talk in a few states of introducing both universal health care and net neutrality as state laws. This will be an interesting experiment, and will let us see whether the sky does in fact fall before rolling it out nationwide.
Wikipedia says Taavi Kotka was a driving force. Does anybody happen to know if he's on HN?
FTFY
It absolutely is a battle we can win.