Funny you should mention that because I only ever play EU4 on speed 1, mainly so I can just leisurely click around all the different sub-systems without worrying about stopping and starting all the time. But that slows everything down - the real impact of slow space travel is everything else moving at normal speed but just with vast gulfs of space between.
One game that does this well is Distant Worlds (especially if you start on a 15x15 map with scattered clusters). I’ve played that to death however and now I’m just looking forward to DW2.