The main use case where I've wanted something like that is that you want to pair an interactive chart with a data table. For example you create a crossfilter and want the table to list the observations that pass the filter.
I actually contributed an example to the Altair documentation that links a table to a scatter plot.
I agree though that the tables are hard to make and not very nice looking. I think it's just not really an intended use of Vega.
