Ever since they introduced Career and Science modes, I've been using them as a guide to ease out the otherwise overwhelming choice of engines and fuel tanks. Having to unlock the tech tree not only makes the vanilla game somewhat more pleasant (and suitable for roleplay) - my now unburdened psyche can suddenly deal with tons of more parts coming from mods.
Totally agree with career mode being a great guide to the tech tree, but it also stopped me from doing grand tours and the like. Just never got that far and tended to start fresh after putting the game down for a while. Self-imposed challenges like no save scumming also didn't help, though.
