Hi jack, welcome to OSM. You're right, that South Portland (and the rest of Maine) has poor data quality for buildings and points of interest. Bad news: There are only a few people doing much mapping in Maine, and I don't think anyone is focusing on buildings in SP. Good news: This is something that you can work on and I'd be happy to help you get the tools you need. If you're interested in connecting with other mappers, and getting help addressing big issues, check out the slack channel: #local-maine (sign up at https://slack.openstreetmap.us/)