To be a devil's advocate, how strident would third party enthusiasts decry a two-party dominated system if it were a different kind of two-party system? What if the two parties on top were rather different and more diversified than our current two conjoined fraternal twins? What if smaller third parties could win more seats in "more local" elections and more voice in all elections?
This is what I believe would emerge if we pushed for the use of multi-seated elections in "more local" elections and two-stage elections in "less local" elections.
Such a system would increase our learning by doing or greater civic participation in "more local" elections and it might actually stand a chance of emerging in the relatively near future, since the rumors of / hopes for the demise of two-party(or even better one-party) rule in the US are quite exaggerated / deluded in my opinion.