Utilizing your fleet in some capacity beyond simple combat is a great idea, however I feel using them as resource automatons is one step too far. I'm not opposed to the idea of sending them off as scouts to survey uncharted regions that you don't necessarily have the time or fuel to visit though. This puts the onus on you as to whether it's worth it to go explore their recon findings. I don't think it serves the gameplay for your fleet to be on automatic mining duty because most of them simply aren't designed with that purpose in mind and it takes something away from you as the player on an adventure.
Also, they may not necessarily survive out on their own against unknown odds. The act of going on an expedition, whether for resources or intel, is not something that should be taken lightly; risk vs. reward should be made clear to the player, with big paydays being fraught with danger. Part of the experience of an adventure is in not delegating or automating too much of the core gameplay to NPCs. The various elements that made up SC2 were basically all player-driven mini games in and of themselves: combat, resourcing, exploring. One step too far into the realm of strategic automation and it starts to become a 4X/RTS game and I don't know that I want NPCs doing too much of the work for me.
A big part of what makes an adventure is the weight of your decision and its dramatic impact. If you did have the option of sending fleet out to recon, which parts of your fleet would you keep under your wing for additional protection, versus sending them out for intel at the expense of your own safety? Or at the expense of their own safety? Out on their own they might be far more vulnerable, and therefore using them for recon could be extremely risky as you may never see or hear from them again.
While it was confirmed above there aren't any XP "requirements" I don't think that should preclude experience serving some kind of purpose. The idea of unlocking new tiers (technology upgrades, new ship types, areas or exploration, etc.) as you accrue experience could be interesting if done right and I wouldn't be opposed to it. I know that's likely to be a controversial opinion with this game but experience leveling is very common in modern gaming and I think it should be adapted in some capacity.