The 20:05 arrives at 20:55; the last evening train to Rome leaves at 21:30. That would be a very risky connection, to say the least, and waiting for the 4:07 train at Napoli Centrale is not something I would wish on my worst enemy.

I was interupted at work - can you imagine - and didn't get to finish my last travel time estimates, but it looks like I was pretty close based only on memory!

Anyway, in my opinion - is a 4 hour visit to Capri and POSSIBLY the Blue Grotto worth this effort and expense? No.
Is Capri nice? Yes. Pretty? Yes. All it's cracked up to be? No. More beautiful than many, many other lovely spots in bella Italia? No.

I visited and stayed 2 nights during a week long visit to the Amalfi Coast (my second). It was nice, overpriced, overrated. Views on the Amalfi coast and Ligurian coast just as nice. My most enjoyable thing on my visit was the 2 hour small boat tour around the island. Mid-Oct, perfect, beautiful day, but the seas were too rough (on that side of the island) to go into the Blue Grotto. We were able to see the same effect in another cave area, although on a lesser scale, I'm sure. On the other side of the island, where the Faragolini are, it was very smooth.

Just my opinion. I would not go to the trouble you plan to visit. I would go again, but only if on a southern Italy trip and if I took a private boat to Marina Piccola (avoiding the crowds at Marina Grande) and parked myself in a private villa for a few days (avoiding the day tripping hoards and tour group baggage carts in town)!

I agree with Dayle.

But if you decide to go on an organized tour, find out their policy/plan in the event the ferries are cancelled either before you reach the island or before you've returned to Naples. How late can you cancel your reservation and get your money back?

FWIW, I think the gardens of Villa d'Este (Tivoli) in the spring when the fountains will be at their best would make for a better day trip. No reservations required. Just go if/when the weather looks good.

I have to agree that Capri isn't what it's cracked up to be at all, BUT...if you have grown up hearing about it and wanting all your life to go, I can understand trying to get there in one day. It really isn't a great idea, but if you have it deep inside of you to go,then you should go. If you feel it's something you can do the next time you go to Italy and want to center in the Amalfi/Sorrento/Naples area, then I definitely would wait.

I didn't read everything, but is there a reason you can't stay in a hotel overnight in Naples?