I think a matching level of emotional investment is hugely important.

Do you mean to imply that a person should have similar relationships to their job and significant other? If so, can't say that I agree.

What exactly are you thinking? Is your point that it couldn't possibly apply to a romantic relationship, or are you thinking it could?

I'm thinking that there is a similar dynamic going on in romantic relationships. There are people who choose a partner for other reasons beyond strict love or money. For example, you might want a partner who is at home and supports you and your work (traditional household model). In order for this relationship to actually support you, like ioseph said, a matching level of emotional investment is important. Otherwise you're too dependent on your partner and that won't work out in your favor. I hope I could clarify my train of thought a little.