Among the reforms, the one that would least affect political diversity would be preferential voting above the line. Since people would be most inclined to engage in preferential voting above the line if they got wind of shonky preference deals by their first preference party, it would substantially reduce the appeal of preference deals across wide ideological gulfs.

As far as a 1/10th of a quota threshold, that is about 1.5% of the vote, which is a lower threshold than any proportional representation system I am aware of in Europe (though I am far from an expert on the subject) 4% and up seem to be more normal thresholds, and are compatible with quite diverse Parliamentary party coalitions.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.