Many of the major attractions in St. Petersburg and the surrounding areas are historical and were rebuilt after the siege of Leningrad, though at great pain due to difficulty in raising funds to do the restorations. The city thrives on the more world renown cultural heritage (ballets for example), and many of the old soviet performers are still draw huge crowds and fill arenas/auditoriums. Many older Russians I've met look very fondly back at the USSR; younger generations have a mixed attitude, many just echoing their parents' sentiments, others enjoying modern Russia.

As far as preservation goes, I think it depends on just how crappy it is. There's a few buildings downtown in St. Petersburg that are the last few that were directly involved in the Siege of Leningrad (remnants of former buildings) and there is discussion on what to do with them - knock'em down and replace or restore as a historical site. It's prime area and the buildings weren't of any importance, but at the same time, the history of WW2 is just really tightly woven into pretty much everything, so there is some deadlock on what to do. Much of SPB was rebuilt to "it's former glory" after the siege so there is interest in restoring what was lost. But it also hasn't stopped gigantic shopping malls from being installed downtown in these spaces, with the exterior of course matching the surrounding architecture.