Totally worth it, even if to just add momentum to building space infrastructure and increase world's competence in space technologies.
Things have changed quite a bit over past 20 years. Launches are getting much cheaper now, and satellites are getting smaller. I imagine costs could be brought down, especially if the scope of the mission was limited to e.g. simple constellation for radiointerferometry.
For an idea of scale, the entire VLA was built for ~80 megabucks. The entire Atacama Large Millimeter Array was built for 1.4 gigabucks.