Is Arena de Lutece worth visiting?

I think it is worth stopping in for a short visit, especially if you are in the neighborhood anyway. It does feel like you are stepping back in time when you walk into the quiet arena. I also enjoyed going to the nearby Jardin des Plantes, which is only about a 5 min walk away.

I agree with all that Dawn said. And, unless you've been or are planning a visit to Rome, when else might you get a chance to see an actual Roman amphitheater?

It is definitely worth visiting if you're in the area. My goodness, it's a 2nd century Roman ruin right in the middle of Paris. If you can appreciate that, you'll enjoy seeing it.
On the other had, I don't think you would travel to Paris just to see it - unless you're an archeologist.
It is both very interesting and slightly underwhelming for the same reasons - the partially reconstructed remains of an ancient amphitheater in the middle of an otherwise ordinary neighborhood. It sits down into the earth rather than rising above it, so it would be easy to walk past and not recognize it for what it is.
Your post makes it sound as if you're the type of person who will really enjoy visiting the site. We did.

I would say, only worth it if you pass by. It is a short side trip from Jardin des Plantes, a bit longer from the Pantheon. It is heavily rebuilt and there is no way to tell how old it is once you're there.

Definitely worth visiting if you're in the area and interested in ancient sites -- though a lot of it is reconstructed. An oasis of quiet in a bustling neighborhood. You needn't spend very long there, work it into a walk through the Latin Quarter or the Contrescarpe area.

The RS guidebooks don't try to be comprehensive like many others do. He "helps" you by choosing only the "best" sights, neighborhoods, cities, and regions. At the same time, he acknowledges that he's being selective and urges you to explore further and find your own favorites. Ten years ago the book listed hotels and restaurants in the Latin Quarter, but newer editions leave them out. When I plan a trip I use RS guides a lot, but also Lonely Planet and sometimes others to make sure I'm not missing anything that might especially interest me.

Hello
I think the Cluny museum romant baths are much more authentic, as the Arènes de Lutèce were heavily dismantled in the 19th Century, and then rebuilt, so don't expect the colosseum, but just a nice garden with more history in it
I wouldn't go out of my way, but it is nice if you are in the Latin quarter

I usually stop by when I am going from the Metro stop to the Jardin des Plantes and it cracks me up because there are almost always kids playing soccer there.

In a diversion from your actual question, I did some research a few years ago and developed a walk of Roman Related sites in Paris based on citations from various websites. I did not include the Amphitheater because I'd been there and it was a slight diversion off the route. IF you are interested, I'd be happy to share my outline with you.

It is not much if you have seen other Roman amphitheaters -- but if you are walking around the Latin Quarter worth a quick look in. Not a bad spot to eat a picnic lunch. We stumbled on it years ago and it was a happy surprise -- but as amphitheaters go -- not much -- heavily restored.

Gogglemap it. It is an ampitheater shaped area of dirt. I was there in November and very disappointed. There is a plaque outside of the entry that had an idea of what it might of looked like and that was actually more interesting than what was left. I've been to about 6 Roman ampitheaters and this has virtually no structures. Check youtube for videos especially if you are on a limited timeframe.

I stayed at a hotel nearby in 2017. Having been there, I agree with Rick Steves about leaving it out of his guide. It is not a fantastic outdoor site. It’s sort of a park and it’s cool to see that residential buildings surround it but it is not worth a trip across town unless you are in Paris for a very long stay. If I recall correctly, I saw teens practicing skateboarding in the walkway around it and I enjoyed that dichotomy more than the ruins themselves.

Bear in mind Paris (or Lutetia or Lucotetia at the time) was an extremely uninteresting city for the ROmans, not a capital city or whatever, just a small 5 000 to 10 000 people maximum, so do not expect the ruins to be overwhelming

I was just there this past week and having previously visited Rome and Pompeii, it was underwhelming. I was walking back from the Marie Curie Museum, so it wasn't far out of my way which make it OK. To be honest, it really looks like what you do see was mostly re-built.