There is a lot that can be done. City ordinances. Land owners in many cities (including Detroit) are required by law to maintain minimum standards of presentability. I think some cities even have specific laws requiring that buildings be occupied to a certain degree. Places like Grosse Pointe have neighborhoods with especially strict rules about how your property can look, from the type of brick and style of fences/gates to the length of your grass and the types of lawn ornaments you can have.
In Detroit there are requirements that the land owner keep the yard, sidewalk, and street free of trash and debris. Weeds on the property above a foot tall are also a no no. There are also regulations about abandoned vehicles, alley maintenance, etc. Residents could lobby the city to increase enforcement of these laws, or raise the standards entirely. In fact, there are plans to at least increase enforcement for the Super Bowl, so we may see some improvements from that within the next year.
With the proper regulations, the city can leverage capitalism to have buildings used in ways beneficial to the city. If it costs more to maintain an abandoned building than to rennovate or sell the thing, "investors" won't leave them like they are now.