I will trying to do this in Fall, 2019. Mainly attracted to the "no visa needed" set up. Has anyone done this recently? Was it worthwhile? Were there good tours available when you got there? Thanks in advance!
I'm considering this as well, and I wonder if you'll get a response if you post in the Russia section.
I did it in 2016. Really lot of fun - I mean, even the ferry trips, which I was nervous about. (I had never slept on a ship before.) I didn't book any meals with my ferry ticket - there are restaurants and snack bars on the ferry itself; just show up and eat and then pay. I booked my own hotel separately with Booking dot com (one called The Library right at St. Issac's). When I checked in in Helsinki, I simply showed them a copy of my Booking dot com reservation. Today when you book it I'm told they warn you they may not accept some reservations (e.g. AirBnB not acceptable, something I think people used to be able to use), but they don't prevent you from booking the ferry without a hotel. I think they just want to have you use their booking system for the extra commission. But the ferry is technically responsible for you while you are in Russia without a visa, so they do want to make sure you have a legitimate hotel somewhere in town.
St. Petersburg was great. Once I got off the ferry and through immigration, I took the "city tour" (just a shuttle van) into the city and was on my own for 2.5 days, then took the same van back from St. Issac's square back to the ferry port. No trouble at all.
I used Google Maps on my phone (I had a working phone in St. Petersburg) to navigate everywhere, walking and by bus. Didn't take any tours. Visited both the Hermitage and the Russian Museum, even though I'm not really a "museum person."
St. Petersburg's beautiful buildings are all lit up a night. So go out and walk at night, especially along the Neva - pretty buildings along the river. You might even be able to take a little river cruise or something. (When I was there it was June so didn't get dark - and then barely - til almost midnight. Shouldn't be a problem for you in the fall.)
There is at least one long multi-year Trip Advisor forum thread about the "visa free" trip to St. P. I suggest googling it for the latest on how the trips work these days - a few things may have changed since I did it in June 2016. (The St. Peter Line is now owned by Moby for one thing.)