Maybe. Is your tv a DLP or just a rear projection (over 5 years old). If it is a DLP then yes, Bluray will look great because a DLP set is at the very least 720p and many are 1080p, which are the resolutions of Bluray discs.
If your tv isn't DLP, then no. Bluray will not look any better than a SD DVD because your television can only produce a 480p resolution.