Touring with any licensed guide, Regent, Denrus, Red October or any independent guide an individual visa is not required. They do a group type visa and just need minimal information, Passport numbers etc.

It is complicated and expensive to get a visa. For most people not worth the trouble. If the ship parks way out often difficult to get to taxis outside the pier. If the ship offers a shuttle service to town then that really helps. Regent has been offering a shuttle service for those with visas.

It is really difficult to do any of the key sights like, Catherines Palace or Peterhoff independently. Here you REALLY need a guide. The public lines are LONG and all Russians it just does not work. Groups go in a separate entrance.
We did it once to check it out I do not recommend this at all.

However that said, I have had visas a few times before and I always enjoy having the freedom to do the city of St. Petersburg on my own. It is very easy to do the downtown sights individually and I always enjoy just walking the streets and shopping at the little stalls with no time clock telling me I have to be back at the bus at XXXX.
Getting a taxi is easy and cheap.

For a first time visitor I suggest the tour route and forget the visa. If you are a second time visitor, have an adventurous spirit you might think about it.