I will probably not be popular here but I really do not like the way the career mode works. Now this may be a mindset thing here, My enjoyment with Kerbal is experimenting with designs and performing tricky maneuvers. In short to me its about the journey not the arrival, but its only the arrival you get a reward for. There is no reward for complex flight planning and test flying. Surely this should be the very basis of science for a space career. I recently performed a probe mission to Duna. I launched from Kerbin, did a sling shot maneuver around mun then a partial aerobraking into Duna orbit. I landed and with 4 experiments (- the transmission cost) I netted about 75-100 science. To me this should have been multiplied by the number of SOI changes in the journey. Think of the scientific impact of the early mars landers this was no trivial achievement. I think a better system would run on 2 levels. Firstly the science level similar to what we have now but with some tweaks and additions. The second level would be efficiency of parts. To start with you would have a basic engine, a basic fuel tank, some basic fins and a gyro stabilizer (think V2). All of their efficiency would be around 50% this would mean they would develop 50% of their maximum power. Every time you use something you a). Get a trickle of science (1 per 10 km traveled or something) distance per point would increase over time, . the efficiency would go up by a random amount which is maxed at say 1/3rd of the gap between current levels and maximum (so you can never actually achieve 100% efficiency). Each time you unlock a new set of parts their efficiency is at 50%. This would change the onus to encourage test flights and unmanned flights to improve your capabilities.