Eh, I actually think that a strong enough libertarian segment led by Ron Paul would force compromise. Imagine, say, a voting bloc in line with the Cato Institute's numbers cited before, 10-20% (we'll say 15%). Give your communists about 10%, split the 30% of Republicans left between secular authoritarians and religious authoritarians (gonna guesstimate a 12/18 split), rest is Democrats.
That's 45% Democrats, 10% communists, 15% libertarians, 12% secular authoritarians and 18% religious right. You'd probably see the 30% of establishment right Republicans cooperating, so there's a 45-30 split with our 25% deciding the majority, super majorities, etc.
Would compromise be easier? No, not necessarily, in fact it would almost necessarily be more difficult owing to the increased number of ideologies represented. But again, that's good. You and I, and people of our political alignments, get to be the kingmakers. That forces the establishment to compromise with us. This can only be a good thing in my eyes.
Situations like Belgium are bad, yes, but also few and far between. In fact I think citing Belgium as an example of why not to have multiple parties is equivalent to me using the hypothetical example of one religious evangelical party controlling everything as an example of why fewer parties are bad. More realistically I'm imagining something like what my friend (German major, visited Germany twice, going a third time and follows German news daily) describes German politics as: some 4-6 ideologies, each represented by a political establishment of their design, jockeying to shape the country's policy. I think their deadlock is actually much better than ours...
Anyway, just my thoughts on how to fix the 2-party debacle we have now.