If your incubator slots are full, you can block yourself from getting whatever the next incubator is.
If you speed up the incubators won in battle you get a small amount of random boost based on the incubator.
A 15 minute costs you 3 hard cash = 1 random boost.
A 3 hour costs you 30 hard cash = 2 random boost.
An 8 hour costs you 80 hard cash = 3 random boost.
Battle incubators drop in a pattern of 3hr, 15 minute, 3hr, 3hr, 8hr. To open this all up it is 173 hard cash to get 10 random incubators. Every 5th time you get an 8 hour you get a 12 hour or 24 hour instead with the 4th time being a skip. Pattern is 12, 24, 12, 8. The 12 and 24 hour cost 10 hard cash per hour but give no boost. So if your slots are full you won’t get them. This lowers boosts cost. If you buy everything it averages out to 1940 for 100 random boosts. Skip the 12 and 24 its 1730.
Skip the 8 hours and it is 7 random boosts for 93 hard cash. This averages out to 1329 hard cash for
100 random boosts.
Skip everything but 15 minute ones and its 300 hard cash for 100 random boost, but that is a heck of a time commitment.