Okay one issue that can never really be overcome with HSR is the train's maximum speed. There have been records for this kind of travel of about 300 MPH. That is really pushing the limits of how fast you can propel any kind of train. When reaching that speed, the friction between the tracks, wheels, and air resistance become limiting factors.
The beauty of Maglev is that it can potentially be free of all forces of friction and drag. Those systems that operate today are held back at ~350 mph because of air resistance. Any faster and you need more energy to overcome the air resistance which becomes more significant at higher speeds. Then there comes another issue in regards to that... noise.
The other major benefit of maglev is that it is quiet, but that advantage is negated when air resistance generates more sound than the friction between track and wheels. By creating a vacuum tube, you have the potential to speed a train beyond the sound barrier. Less air in the tube translates to a greater potential speed without the sonic boom. So the potential for maglev can be upwards of 6000 mph where HSR is at the best 450 mph before track friction becomes too high, not to mention the sound barrier becomes a factor.