They are quite different, but both worth a sniff. And possibly a purchase if the price is low.
Spark is part of that sweet/light/spicy trend that has been popular for the last two years or so. It is pleasant enough, not at all offensive, and works well for someone who wants a little warmer scent for the fall. You could wear it to work and no one would complain.
Blv Notte is an entirely different animal. Rich and very unique - it really smells like nothing else. Warm ginger notes, a trace of chocolate. This is much more an evening scent, and very suitable for clubbing, dinner, whatever. And women like it, in my experience. These are the good points...However, like most of the Bulgari line, I think the notes smell pretty synthetic, and it gives some people a headache. It is not subtle. I would encourage you to find a way to try this out before you buy. I think most folks would be happy with it, but personally, I grew tired of it pretty quickly. It just got a little cloying and it began to seem somehow overdone. So, overall, a mixed review.
You will get more passionate viewpoints about this one. I predict that folks will be fairly neutral to positive about Spark.