Residents experienced shock and awe when Miami administrators used public money to actually build something decent in Model City, one of the poorest neighborhoods in the nation's poorest city. This $3.5 million, one-story facility is so nice that even Commissioner Art Teele is proud to hold public meetings there at the Black Box Theater or the big new carpeted conference room. So are the prestigious board members of the Model City Community Revitalization Trust, who are planning an artful low-income housing renaissance nearby. A local homeowners association provided some of the pressure to make the community center a reality and now has an office in the building. Some people miss the old boxing gym that once stood on this land, but you can always find a garage in which to punch. You can't take swimming lessons in a garage, however, but you can do that at the Miller J. Dawkins Swimming Complex at Hadley. There is also a fitness center for kids of all ages and a walking track and aerobics classes for seniors. The center is open from 7:00 a.m. to 10:00 p.m. weekdays; 9:00 a.m. to 5:00 p.m. on Saturday.