Definitely agree with most previous posters. I have been to S-P twice and if you have the slightest interest in architecture, art, culture, or just want to see something beautiful and different from anywhere else (in Europe or even in Russia), then it is worth a visit, for sure.
The only area which I don't think it outranks any of the big European capitals is in high-end cuisine. You can eat well, but if you're after different types of high end restaurants, well, S-P is no match for other places in Europe. In anything else, especially in the arts and architecture department, it is second to none. It is also a very manageable city for people (distances are not huge, streets are made for people, not cars).
You say that you're not interested in Moscow - I know what you mean, I don't like it as much either... but I would still tempt you to give it a go. It is completely different from S-P, less friendly, more metropolis than city. However, it is also quite different from anywhere else in Europe or Russia, and worth a few days. I find that I like S-P more, but I tend to find more reasons to visit Moscow than S-P, it's bigger, busier and there are usually more things happening there at any given time.