After you get the Gravity Suit back and get the Power Bombs, you can go back to Brinstar, Kraid, Norfair, etc. with the new upgrades. Go to Chozo Ruins (green unmapped part) and to the lower part. You can get a Super Missile Tank. There is a long path that leads back to Crateria. You can use the Power Bombs and get more items. You can travel back and forth to Chozodia if desired.