Xyd

Don't be daft! Nothing wrong with being careful with your Kerbals. Sooner or later there will probably be some sort of punishment system in place for needlessly killing Kerbals, so might as well get into the habit of not sending them to their deaths so easily. Regardless, ever since I played KSP, even in Sandbox I'm extra careful not to put any Kerbals in unnecessary risks. I tend to test everything remotely first before I resort to using a Kerbal, and I always tend to build an escape tower of some sort. As someone else already stated; it adds to the immersion. Also, as a result of doing the above, if you ever do suffer a catastrophic accident and a Kerbal/Kerbals die as a result, the impact of that death is more pronounced.

Further fleshing out the science of the game including more scientific instruments and improved feedback from that. Make probes more useful along with space stations such as conducting ongoing research. Implement the economics within the game so that we now have currency to manage. Biomes for the other planets. Further enhancements made to career mode including optional missions and perhaps Kerbal public perception that could affect what missions you get along with your funding.

Test fly things? Hmm, that's the first I've heard about that, so a testing chamber of sorts then? Something I've seen suggested before, and something that I really want in the game. If the ability to test things is coming in the next update, then I'll be even more pleased..