Umbrella is actually a really good song, aside from the fact that Rihanna's performed the original version (whom I actually like a lot), it's an awesome song from a musical standpoint, it has a great melody. I mean, there are so many covers of that song, it's just a testament that Umbrella itself is a great piece of writing. Mandy Moore, Plain White T's, Scott Simon and others have covered the song, there's tons of covers up on YouTube.
Don't knock a song because you don't like the way it was produced and performed, there a lot great songs from a writing stand point that don't always have the best production.
And besides, Umbrella will be remembered more often than most of Vanessa's work, I gaurantee that, and it's only because Rihanna's more popular. *Shrugs*