Well, i would say to fight fire with fire.
As such, if they are not looking after the land but anyone can build on it......you should go build on it first and put something tasteful there. Need to be pro-active, otherwise more motivated people will beat you to it and this sort of thing happens.
Of course, that wont stop other people building on it, but it may well make them less likely to do so, or might fool them into thinking the land is being maintained, so they look elsewhere.
Otherwise, i agree with the posters above who suggested you file a ticket about it all and ask the lindens to set an auto return.