It seems like everyone is thinking about the balance as a game mechanic rather than who the feature is targeted toward.
Short range :
Casual player can't afford the credit or time investment. Expansion of the bubble is barely noticeable to them, their gameplay is the same.
Large BGS power gets more space to expand into to make their system count Line Go Up.
Coordinated Power Play groups get more space to move into, maybe more tactical decisions.
Explorers want to colonize their five Earthlikes orbiting a gas giant orbiting a neutron star 20kLy out. Since it will take them longer than the reasonable lifetime of the game to reach that, they don't touch colonization.
Medium range :
Casual player can't afford the credit or time investment. Maybe they use some outposts leading out of the bubble to try out exploration for the first time.
Large BGS power gets the same space to expand into to make their system count Line Go Up. They can also use the increased range to wrap around expanding opposing factions and cut off their expansion.
Coordinated Power Play groups get even more space to move into, definitely more tactical decisions.
Explorers can now reasonably reach the far away places they want to go to, but only if they work in groups. Will still be a multiple year commitment, putting off many.
Long range or unlimited :
Casual player can't afford the credit or time investment. They still don't notice the change except on the fringes of the bubble, and get more options for exploration.
Large BGS power gets the same space to expand into to make their system count Line Go Up. More options for connecting systems for expansion, and can directly compete for more valuable systems.
Coordinated Power Play groups get even more space to move into, and can directly compete for more valuable systems.
Explorers will now be fully invested, reaching deep space locations quicker and spending their time creating mini bubbles around interesting discoveries. BGS and Power Play groups may even see some of these and try to build connecting systems to take them over.
If this is for more bubble systems that only the biggest groups are going to hold onto, just wave a magic plot wand. If this is for explorers, the range has to be large enough to be useful in a reasonable amount of time. If this is just to create a money sink, it's not going to be effective in any meaningful way - make new ships or other new features require materials that didn't exist previously, so a new player and someone sitting on hundreds of billions of credits have the same "grind" to unlock it.
Short range :
Casual player can't afford the credit or time investment. Expansion of the bubble is barely noticeable to them, their gameplay is the same.
Large BGS power gets more space to expand into to make their system count Line Go Up.
Coordinated Power Play groups get more space to move into, maybe more tactical decisions.
Explorers want to colonize their five Earthlikes orbiting a gas giant orbiting a neutron star 20kLy out. Since it will take them longer than the reasonable lifetime of the game to reach that, they don't touch colonization.
Medium range :
Casual player can't afford the credit or time investment. Maybe they use some outposts leading out of the bubble to try out exploration for the first time.
Large BGS power gets the same space to expand into to make their system count Line Go Up. They can also use the increased range to wrap around expanding opposing factions and cut off their expansion.
Coordinated Power Play groups get even more space to move into, definitely more tactical decisions.
Explorers can now reasonably reach the far away places they want to go to, but only if they work in groups. Will still be a multiple year commitment, putting off many.
Long range or unlimited :
Casual player can't afford the credit or time investment. They still don't notice the change except on the fringes of the bubble, and get more options for exploration.
Large BGS power gets the same space to expand into to make their system count Line Go Up. More options for connecting systems for expansion, and can directly compete for more valuable systems.
Coordinated Power Play groups get even more space to move into, and can directly compete for more valuable systems.
Explorers will now be fully invested, reaching deep space locations quicker and spending their time creating mini bubbles around interesting discoveries. BGS and Power Play groups may even see some of these and try to build connecting systems to take them over.
If this is for more bubble systems that only the biggest groups are going to hold onto, just wave a magic plot wand. If this is for explorers, the range has to be large enough to be useful in a reasonable amount of time. If this is just to create a money sink, it's not going to be effective in any meaningful way - make new ships or other new features require materials that didn't exist previously, so a new player and someone sitting on hundreds of billions of credits have the same "grind" to unlock it.