Like I said in another post, I'm pretty new to this game, had it a week or so. I've done all the campaigns and several ordinary games on different map sizes and with different races. Currently the things about the game that I feel I understand the least, and perhaps matter the least or are ignorable, are trade routes and tourism. I even made a custom race that takes two negative points in both of those to place benefits elsewhere.
However I could be wrong about them. Are they really worthwhile? How much money do I leave on the table by ignoring them? Also factoring in opportunity cost - in other words, in the time it took to research trade route upgrades, what did I sacrifice by not researching something else, or ships built rather than freighters, tiles built rather than trade or tourism buildings. Is a wealth generating tile really worth much less than a tourism tile?
How do you even maximize trading? Should all trade routes originate from the same planet? Should they all target the same rich planet, or is there some sort of diminishing return (or is it even possible to target the same planet again)? Should I not bother with trade buildings on planets that don't sponsor routes, or do they provide some benefit anyway?
If a planet has a +2 tourism tile, should I always build a Port of Call on it, even if it means sacrificing other adjacency bonuses?
I just feel like the utility of these features is pretty nebulous, and I've been functioning fine without them anyway. But I'm open to learning more about them.