We were on the Renaissance R8 Baltic cruise 3 wks ago. We took the ship's tour of the Hermitage and the big advantage was that the tour groups had access to the Hermitage a few hours before it was open to the public. I would guess that the crowds are larger now with the peaking tourist season. After the general public entered - it was crowded. The trip and tour were great.
An unexpected treat were a truly professional dockside band (the St. Petersburg Dock Band). These guys played their hearts out and were great. They play for donations - musicians of their caliber sadly have to do this for an income.