Just writing here a few considerations.
We know that a +100 boosts cost 2000 HC.
We know that every 3-hour incubator has a +2 on a single stat (unless I’m mistaken, but I don’t remember incubators not having a boost in them), a 15-minute incubator has a +1, an 8-hour has a +3.
Now, if I spend 2000 HC on boosting 3-hour incubators, I get 66.7 free incubators (2000 HC divided by 30 HC, the cost of opening an incubator). 66 incubators will give me a total bonus of +132, 32% more than what I pay for a +100 stat boost. And I get coins, and DNA.
You don’t obviously need to speed up the 15-minute incs with cash.
And you won’t obviously speed up the 8-hour incubators.
So, while you have an 8-hour (or longer) inc slowly roasting, just keep playing and speed up the other incubators and (if paying for boosting is your thing) you’ll get more bonuses than paying in Ludia’s shop for their boosts.