I'm looking for more concrete info, though.  In particular one thing that seems a detriment to tourism is that you're not going to get a lot of adjacency bonuses.  If the choice is between a tourism building, vs. a wealth building that gets +3 from other wealth adjacencies?  I don't know.  How do the numbers work out?

If you are Benevolent, all the bene point builder buildings give Adj bonuses to Tourism.   Tourism also gives Adj bonuses to wealth, so that's an easy one to put it by as well.

I'm not enough of a min maxer to have done the math and done a focused comparison.   I just know that by the end of the game tourism is usually my largest source of income when playing any bene or pragmatic race.

Hi, I am not sure this counts as concrete info either but here is how i play:

I ignore the savings income. The spending sliders constantly sits on 45%/45%/11% with 11% in wealth so there is no coercion. I don't build economy planets, I live of what I have, find from anomalies and diplomacy as long as possible and then start investing in trade when it is convenient. All trade routes will lead to one plant, which most often ends up being my capital. Furthermore I only very rarely go with the pragmatic tree which has boosts to trading.

Eventually I will also get tourism since I don't have to invest tiles (or only isolated ones with no adjacency anyways) note that you also get +(20%?) tourism from the highest approval starbase modul. What's also nice about tourism is that it comes from the approval tree, which is very convenient for me, since I usually play for large populations.

This usually easily covers the cost of my fleet... but then again I usually am not the starting the war or joining in the arms race in the first place. I much rather prefer to ahve many research worlds .

Advantages and disadvantages of trading:

+ a good trading partner very rarely goes to war with you
- trade routes grow over time, conquering your trading partner will cost you bc in the long run.
+ It occupies only 3 tiles in your empire if you only get the explicit trade buildings (+starbase upgrades around that world, but this is in the economics tree anyways)
+ no need to reasearch the economics tree

I don't know what the numbers are that speak for economics, I used to do one or two economics world in the past, but I don't remember it being that much better, but this might just be me.

In terms of how to set up your trade routes, Maybe you want to take a look at the TradeRouteDef.xml, I will only quote some stats:

<PlanetIncomePercentage>0.05</PlanetIncomePercentage>
<PerTileBonus>0.025</PerTileBonus>
<PerTurnBonus>0.1</PerTurnBonus>

The per tile bonus is related to the distance of the two trading worlds I believe. So 40 Tiles of distance are +1 income. The per turn bonus means that trade routes get more effective the longer they are there. For the planet income one I am not entirely sure what it does or whether it corresponds to your or your partners world or both.

Trade routes can easily give you +100 bc per turn per route in later stages, with the bonusses from the buildings.

Last I looked into it, it appeared as though base tourism was a function of average planetary population throughout the galaxy, and was independent of influence and 'culture.'

Are you sure that the cap is 250 credits per trade route? The only limits I see within the XML files are on contribution from trade route age or trade route length to the base value of the trade route, and the bonuses to trade route value would be applied after these caps, not before. Contribution from planetary "income" appears to be uncapped and is a percentage of the total production of the two worlds connected by the trade route.

As far as actually hitting the age and length limits goes: Hitting the length limit is impossible regardless of trade route type; the per-tile bonus of standard and slave trade routes is 0.025 and the per-tile bonus of luxury trade routes is 0.05; in order for the route length to contribute 250 or more credits to the value of the route the route length would have to be 5000 or more for luxury and 10000 or more for standard or slave trade routes, but the diagaonal of an Impossible map is only 761 tiles and the minimum pathlength between any two points is very unlikely to be much higher than that. Hitting the age limit is unlikely but not impossible, as the contribution of trade route age to trade route value is 0.1 credits per turn for all three route types. A route would need to exist for 2500 or more turns in order for its age-dependent value to be limited by the cap.

It's not that difficult for a specialized economic world to get well into hundreds of credits per turn.

The biggest effet to trade, early on, is a small diplomacy bonus.  Combined with other bonuses, it can delay wars with neighbours just enough for you to build a fleet.  The credit they bring is negligeable, but noticeable very early on.  It can make the difference between a balanced budget and a small negative one.

By the time you reach mid-game, by the time you get 6-8 trade routes... that's pretty irrelevant because by then you own the game.

Tourism is a factor of influence.  It's a pretty big bonus mid to late game, by the time you get the tech.  But only if you have large influence.  My advice: build something else until you get a decent chunk of the map (large&above), don't use them for small maps.

I'm not sure what the tourism formula is now, it used to be just population (or something else was more heavily pop influenced) lonnnng ago & the yor could effectively run the whole gae at 0% wealth soon after unlocking it.  tbh I think it's an improvement as is even though I mostly play yor.  if you can do what's needed for tourism, it can give a sizable bump to credits... but otherwise it's effectively just a few free credits/turn at worst.  I've never considered, or tried to makem trade a significant income generator.  the relations bump is wildly worth it though

Don't use these that much so it I'm not sure how effective it is. I do know that tourism is influenced based unless, they changed it it was 1 BC. Per 10 Influence points. Now population is one of the factors in influence that is why you were confused.

Now about trade the further away the trade route the more money you get unless they changed it, that means unless, you find a planet with trade bonuses, or maybe the planetary resources affect this you would be better to have all your routes from two planets the farthest you could have apart. You should be concerned with speed, and range on your trade ships here. But first before you do this build trade ships send them to the closest to the trade planet to get immediate income. Then build better ships to go to optimum distance from your planet to the farthest possible away planet. Cancel one route preferably your cheapest before you reach your destination to have a free route. This vote to be the best way to work trade. Not counting bonuses, resources, or buildings though you would build the appropriate building on the planet.