Thanks for the comment!
Things like gathering stories and trading are designed to give a cash boost to a starting character who may be too weak to do some of the more challenging content. I agree there's (almost) no reason not to always do them early if you can. However, if you collect stories from all 16 planets, it means you've also mapped the entire galaxy, and probably encountered some enemies/events on the way. As for shuttling goods between planets - well, first you have to find those market planets. And if you buy and sell all the available goods, you may find it difficult to complete some quests that require these items later (you can find goods through exploration/travel encounters, but it's not as sure and simple as buying them from the market).
Personally, I think a time limit would clash with the "explore at your own pace" nature of the game, but I know it's a matter of taste and that some people would prefer a tighter challenge.
If anything, I believe the game could benefit from more content that would make more strategies possible. While I won't update 4x4 Galaxy any more, I'm working on another project with the same core idea that will have much more content and variety.