bigger planets take longer to develop obviously, but have potentially greater rewards due to non negligible income from population. feel free to apply my analysis technique (crude as it is) to a more complicated situation, like developing a terran world for population income. you'll probably get a similar result but over a longer time frame. higher initial outlay and longer time to recoup investment but result will be a larger net gain once it goes positive. what i'd be most curious to find out is which is most efficient credit for credit in terms of building revenue.
OK, I did a similar analysis for a 90% Terran (w/3 mines).
premises:
1) the tax income at lvl 2 population (100) from the Terran is approximately 2.9 creds/sec. it takes many minutes to get to this level though.
2) the resource income of each rock is .47 resources/sec. the total income from this is 1.41 resources/sec. it takes 30 seconds and 250 credits to build each extractor.
3) the underdevelopment penalty will subtract 2.0 creds/sec for first 45 seconds, and .5 creds/sec for next 60 seconds while the upgrade builds. this total cost is 120 credits.
4) the cost of building the first infrastructure upgrade is 450 credits, 100 metal, 75 crystal; and 550 credits, 175 metal, 125 crystal for the second upgrade (to get out of negative income).
cost analysis:
your outlay in cost is 450+550+750+120= 1,870 credits
in addition you pay 100 metal and 75 crystal; plus 175 metal and 125 crystal. assume conversions rates of 1 resource = 5 credits (median black market price on quick buy button), this amounts to 2375 credit equivalent.
the total cost, all things considered, is 4245 credits.
Ignoring tax income again, and using only the resource income of 423, means 4245/423= 10.0+.5 or 10.5 minutes payback.
Adding income of 2.9/second from a population of 100, is 174/minute, meaning 4245/(423+174) = about 7.5 minutes payback.
Again, these rough calculations don't properly account for the lower income period while the population is growing.
Ofcourse, there are still 2 population upgrades available for a terran - and we've already calculated that the last one would pay for itself in about 15 minutes (but takes much longer to actually build out).
The benefit of having additional logistic slots available is of immeasureable value, and ultimately may be a bigger factor in deciding whether to colonize an additional planet.