I've heard the theory that we tend to be attracted to people who are genetically different from us too. I think that the experiment that supported that went a little something like this:

Different people have their own unique scent. Apparently part of that is racial (though to assess that you need to control for diet especially when a group eats a lot of curry or chili or fish etc). But part of that comes down to individual uniqueness. I think they presented different cloths with different scents to people and asked which cloth they preferred. They then found that the cloth that was preferred tended to come from the person that was most genetically different to the person doing the choosing. I'm fairly sure that was how that went.

Lots of severely detrimental conditions are recessive so you would need both parents to be carriers for the condition to express in the offspring. So yeah, the thought was that if there was some mechanism for assessing genetic difference (such as pheremones or perhaps phenotype / physical characteristics) and people did indeed seem to be attracted to someone different from them (i'm not sure how much evidence there is to support that) then the reason may well be to prevent those recessive diseases.

(inbreeding is part of the problem behind some of the royal families in history and also part of the problem in increasing the numbers of severely endangered species where we have little choice but to force inbreeding or allow extinction)

It is unclear how much that comes through with respect to phenotype. There are social norms (lessening but still present in much of the world) about marrying someone who is a member of ones own cultural group. NZ is probably less inclined to that social norm than other parts of the world. I remember being well and truely surprised to watch an Oprah episode and hear how the majority felt about 'mixed' or 'interracial' marriages.

With respect to my preference... I think my preference is basically a male version of me. Similar build but the male version. Similar features but the male version etc.