Cinque Terre and Croatia too similar?

I don't find them particularly similar, but I would reconsider depending on your overall itinerary--why waste time to get to an overcrowded place? I would look for somewhere to do hiking in Croatia where you will not be sharing the trail with so many others.

It would never have occurred to me that they were similar, other than both being on the ocean. I love both. Some Croatian towns definitely have a Venetian heritage, so it's not hard to be reminded of Italy while you are in Croatia, but the Cinque Terre as you know is more about hiking between towns than staying in one spot, and they do not feel Venetian to me at all, anyway.

I think in July you'll have crowds in both places. I'd never go to ether place in the summer, personally, but some people have school and work schedules to deal with - understood.

It sounds like the real issue is that your teen wants to go to the CT and you want to do Croatia. Maybe you can talk your child into Croatia - has he/she seen the Rick Steves Croatia videos? (Free to watch on YouTube.)

I also don't think they're too similar but the teens will enjoy either one. Does the trip already include more of Italy or another country? You're probably not going to spend a week in the Cinque Terre.

The two countries are most easily connected by flying, such as between Rome, Venice, or Milan and either Split or Dubrovnik. You can also find nonstop Florence-Split flights in July, but no nonstop flights from Pisa or Genoa airports; www.skyscanner.com.

Agree....not similar at all, except both on the ocean, and we have visited the CT and Croatia.
My only advice re: the CT would be to definitely spend a night (or better two) so you can enjoy the peace of the sun rising over the hill and the quiet of the CT waking up, as well as the very different environment during the evening in any of the CT villages. It is also good to experience the views from the trails between the villages as well as from the boat that connects most of the villages.
Between the places we visited in Croatia and the CT, I like the Cinque Terre more. We visited the CT in very late August (as part of the RS Heart of Italy tour) and Croatia another year in early October (as day trips from the SeaCloud sailing ship, and it was extremely quiet during October).
Tell your teens I said they are very lucky to receive the gift of travel!!! Seriously.

I don't see many similarities between the two - one is a place overrun by tourists and the other is an entire country! Parts of Croatia on the coast will be busy in July, but I have found plenty beaches and coves on the north side of Hvar where there are hardly any other people in July.

You can see where my vote would go!

Responding here a few days after you posted the question but here's another thought: google "crowds in Cinque Terre" and have your teens look at some of the "images" that are shown. I took my then-19-year-old to Cinque Terre 15 years ago before it was so overrun, and he loved hiking and swimming during our three days there. A dear friend went there in 2016 and was stunned at the numbers of people and will never return. In Croatia, if you avoid Dubrovnik during the day (and some of Split, too), you will likely not encounter that kind of crowds in streets, on boats, or elsewhere. July will also likely be some of the worst crowding possible, wherever you go, but especially in CT....

Plitvice Lakes National Park is a mob scene during day-tripping hours, so it's critical to spend the night before your visit in or near the park so you can get inside very early. The walkways get totally mobbed.

I can't compare it to Dubrovnik since I haven't been to the latter recently.