ehm, with all the event buildings nowadays, why would we need extra population if these event buildings also give loads of them? on live, i have a city with 25k free population while no houses are present anymore
There are actually several reasons why population makes sense.
First, There are plenty of casual/mid-tier players that don't complete all of the events, so they would not have the same excess that a daily player would have. Those players tend to rely on normal goods buildings and supply buildings, etc, so the population would help them along. A GB that's useful for a wide range of players is good.
Second, there is a niche of high volume GvGers that run dozens of racks. I have 177k population, and it's all used. Once SAM comes out, that demand for population is going to be even higher. While the majority just use Traz only to fund their GvG fighting, those that need the population -really- need it. For TVP, it would give the most hardcore gvg'ers a reason to build it since the other effect nearly pointless with so few charges.
Third, It does force players of all ages to consider how much the GB is worth to them. Especially in earlier ages, getting enough happiness to offset the population might be tough. with 177k population, I've dealt with city happiness issues regularly. Just 1 building not polished could drop back down to 100%. It's not make or break, but it definitely forces early age player to decide between inno or the more advanced GB. Either way, they would have more population than they could ever use.
Finally, it's not a "no-brainer" type bonus like FPs. If you put FP on either of these GB's they'll become popular. As one of the most prolific goods sellers on my server, it'd make me filthy rich. I'm not opposed to that idea!
It would definitely give all of the defense stacking players a real reason to complain because a much much higher % of players would build it (if we're talking TVP). That alone tends to deter me from wanting FP on TVP. The bonus should be something that isn't a no-brainer but is still useful (coins/supplies are more token bonus than actually useful).