Two benefits of the move, one of which Noel alluded to, are that there will be secured (albeit apparently not free) parking, and the station will be closer to the rest of Miami. I know people who are put off by the fact that the current station is not only pretty far north -- roughly NW 83rd Street! -- but also relatively far away from freeway access, being stuck in the industrial Hialeah hinterlands between I-95 and the Palmetto Expwy. The airport station has easy access from the Dolphin Expwy. And the airport location won't strike the majority of the population down here as being too far north.
As for parking, well, I just R/T'd it to Tampa and back last week on the Silver Star, and there is no way I would have left my car overnight at the unsecured/unattended lot there (or the one in Hollywood for that matter). An actual secured parking garage: sure. As it was, given that my better half was unable to either drop me off or pick me up, I ended up having to use Uber (because like most people down here, I live nowhere near a MetroRail or Tri-Rail station).
So I think this is a positive move. The real problem, of course, is that only rail buffs like me will take Amtrak for intercity travel within Florida. My trip up was fine -- I had a roomette and got lots of work done. The return trip was a disaster. I knew that the Star would probably be running late on its way south, but it ended up arriving close to 3 hours late and had the nerve to lose another hour plus on the way south. My 5+ hour trip arrived 4 hours late. No one is going to sign up for that voluntarily, let alone pay money. FEC/Brightline has talked about expanding to Jacksonville and Tampa after getting Orlando underway. Here's hoping that comes to fruition.