It's frustrating when you are a player mostly interested in space travel, with a car/plane here or there, but 8 of your 10 max contracts are all about flying/land speed. I think a better system would be buckets per type, and you increase those categories individually in that particular section of the research tree.
e.g. you can go further in the rocket tech, and have a max of 5 space contracts, and only 3 car and 3 plane contracts
I realize I might be off on my assumptions about how contracts are categorized, but the issue of "most of my contracts are annoying and I don't want them there but can't remove them" is real.