We did a Baltic cruise last September, visiting Copenhagen, Stockholm, Helsinki, St Petersburg, Gdynia (for Gdansk), Tallinn and Oslo and none were tender ports. It was also easy to get into each city/town - in most places we used the hop on, hop off buses for sightseeing. However, it is adviseable to book either a ship's excursion or a tour with an independant tour operator in St Petersburg. By doing this you are covered with a group visa and do not need to apply for one individually. Also, the ship docks in a commercial port and no taxis are allowed inside the port gates which are some distance away from the ship (only the licensed tour operators are allowed in the port). The main tour operators in St Petersburg are Red October, Denrus and Alla Tour. We booked with Alla (www.alla-tour.com) and we had an excellent two-day excursion, with early entry into the Hermitage Museum to avoid the crowds!! Alla will also arrange evening visits to the ballet and the folklore performance. I think you will find that the costs of excursions with the independant tour operators are considerably less than those organised by the ship, and in most cases you see a lot more. Hope this helps.
I would like to thank Jean Whittle for her informative comments. It makes it a lot easier for us to decide how to plan our visits ashore with our in laws (mother in law has mobility difficulties).
Thank you. I hope you enjoy your cruise - St Petersburg is amazing.