Thassos looks like a beautiful place for people to visit for a week or two. With Romania being one of Greece's neighbors, it only makes sense for them to travel by car. Maybe those Romanians can make their return visits using chartered buses instead? This could help cut down on many of the downsides of travel by automobile, among them heavy traffic.
Given that Thassos is a Greek island, I'm guessing that Thassos has more or less the same weather all year long. If this is the case, then visiting Thassos during an alternate period can provide for an interesting travel experience. August is the traditional or expected Holiday month, so a visit to Thassos in a month such as May or October would offer all the good things about Thassos only with less traffic and more space for people.
I'm just trying to provide suggestions for visitors to enjoy the Thassos Experience without feeling like they're at Disneyworld or some other tourist traps where people spend more time in line waiting than they do actually experiencing life and being there.