Well if space is empty and boring then exploration is boring. What do you find? Planets you may or may not want to colonize, and other races.
You could ditch all that and have everything in sensor/fuel range known. So if you can reach another star system you know what its planets are like. You could then replace exploration with archaeology.
Archaeology would allow you send to research vessels to long dead worlds or strange locations to try and find ancient relics, wealth, and technology. Archaeology takes time and those research ships can be plundered on their way back. So if you find 10,000 gold in an alien vault you still need to get it back to you home world before you get the credits. Pirates and other players could attack the ship and if its undefended it instantly surrenders and switches sides.
Relics might provide permanent bonuses but have long term costs which are unknown so its up to the player to decide if they want to use them or not. The intelligence booster might give you a 20% research bonus but it will be a few decades before people realize its halved your populations growth rate. The bliss computer net might make everyone happy in the empire but each turn there is small but growing chance it will try and take over.