I love Kerbal space program...But...

The entire point of more complex parts is to build space stations and rovers.

Space stations are in fact cool, but aside from using them as a refueling station, they are almost useless.

Ok, you can build rovers yes? Correct. You put a rover on mun. Accept a temperature study mission and start driving FOR SCIENCE!!!
It is 15km away. Your rover is unstable at 20km/h, so you try to keep it at 15. Aaand after 45 minutes of driving you crash.

So, that isn't fun. It is the complete opposite of fun. What else can you do?

You can build colonies. They are about as useful as space stations...

So... there is still one thing. Planes.
In KSP, you can build planes. But why? Once you can make an orbit around Kerbin, you can land literaly anywhere. Not to mention, that flying in atmospheare is 100 times slower, so even if you decide to do a temperature scan mission on the other side of Kerbin, you do not realy need a plane as much as (orbital glider).
And when I did want to make a playthrough using planes and missions on Kerbin to finance space program, I realized, thar researching anes is EXACTLY as expensive as researching rockets.

This game is seriously lacking justifications to use 80 percent of it's advanced features. Newest patch added ability to construct in space. Theiretically great, but there is no use outside of chalanges. You won't go upgrade an old satelite with new science gadget, when a new satelite is easier and better option in every single way.