I loved X2 but it was at a point in my life when I had plenty of time to both enjoy the flying about stuff and put a lot of effort in to the management element.
X4 looks like everything I wanted back then, but I just don't have the time to dedicate anymore so concerned that I wouldn't get the same enjoyment out of it.
Give it a go if you get a chance and as Ratty says, it's often on sale on steam or GOG.
I'll see if its discounted around xmas which is the only time I really buy games now.