Periodically various sections of vice-infested Biscayne Boulevard emerge as the latest darlings of developers and entrepreneurs. At last, these urban-renewal boosters boast, Biscayne is on the verge of moral rebirth and commercial boom. Speculators buy up chunks of the street. And then somehow it just doesn't quite come together; somehow Biscayne is as resistant to reform as, well, as its crack-addicted hookers. Still the signs of new life on this seamy stretch of the boulevard are encouraging. Key is the renovation from 54th to 57th. High-profile restaurateur Mark Soyka, resident of nearby Morningside and originator of the News Café and the Van Dyke, has just opened a new restaurant and gourmet store at 55th, with several other shops to follow. If Soyka can pull off a planned transformation of the gas station of ill-repute at 54th into a coffee-and-croissant market, that just might clinch the turnaround. On the twenty blocks stretching north, many new restaurants and businesses have begun to move in on the kitschy collection of sleazy motels. Wide-open drug and sex sales appear markedly down, though it's still a bad idea to actually walk along the sidewalks at night. You won't be in much danger, but you will almost surely be mistaken for someone -- old, young, churchgoing, no matter the color or sex or sexual orientation -- who is selling or in the market for something illegal.