Lagrange Points are specific to a two-body gravitationally-interacting system. So I guess the question is: which Lagrange points are you referring to? If you are thinking of Earth-Sun Lagrange points, then yeah, maybe you could start to build up through interferometry an aperture approaching the AU scale (not the scale of the entire solar system). There are some glaring problems I can think of:
- You need to actually fill in the space with dishes/apertures to get good resolution. The more inteferometry baselines (pairwise separations of dishes) you have, the better you will do. But you're not going to get much advantage with only handful of baselines.
- You need to combine signals from the telescopes very precisely in order to do interferometry: either in real time, or after the fact using precise phase information about the EM waves measured by each telescope. Precisely measuring the phase information at optical (UV/vis/IR) wavelengths (compared to radio) is very challenging due to the short wavelength. Combine that with the fact that your spacecraft move around (changing your baselines continuously) and it's not obvious to me that we have precise enough positioning/stationkeeping and timekeeping ability to pull this off.