Does that mean I get more hearts or the hearts are worth 10x more?
Each heart will be worth 10x each, so it helps with feeding it into the research machine, level 3 gives you 100x per heart. Obviously the higher the research the more hearts you require so once you get to a certain point you need to upgrade the colonists otherwise research would take too long.
By the way, if you didn't know you can build multiple research machines, you can set them to research the same thing or different things. I usually have 2 bots feeding each machine so they don't interfere with each other too much.
when you put Wuv into the machine, there is a small delay between each, so there is a limited amount of wuv you can put in even if you have infinite resourses, to speed up you will need to create 10xWuv