We have to assume every state will matter. If the nominee is decided as early as usual, then there's no possible way it will be RP. The only way he wins will be to have a long drawn out primary season with multiple establishment candidates staying in the race to the bitter end without conceding. And even if that happens, the odds would be greatly against him, but it's still the case that the longer the race continues the better it will be for him to get people to pay attention to his message.
Every RP supporter should make a point to own their home area and start laying the foundation for him to do well in their own state's primary, no matter how late in the season their primary is. Obviously Iowa and New Hampshire will be of preeminent importance, as they always are. But local activists shouldn't sacrifice opportunities to build support in their areas where they can make a big difference because they only care about the early contests where, aside from donating money, they can't do much. The "All politics is local" maxim is true.
That said, does Rand winning in KY mean that RP can win there? Absolutely not. In a full Republican presidential field, many of Rand's supporters will vote for someone other than RP. The argument that "If Rand can win in a socially conservative state like KY, then Ron can win anywhere." is a non sequitur. Rand is running as a very socially conservative candidate, and social conservatives are not Ron's biggest hurdle anyway, it's the more socially liberal neoconservatives who are.
I'd say Rand has warmed up KY voters to make RP be less marginalized there, and will win him some votes. Ron may even be able to break 15% in the primary there, but not by much.