I will note that I think you mixed up yields and rates in your post. Rates are lower in other countries than in the US, and in some countries (last I looked), there are actually negative rates. So, for example, a corporation can buy German bonds at a negative rate (guaranteed loss if they keep until maturity) or US bonds at a positive rate (guaranteed very low gain if they keep until maturity. So, some transfer their money from euros into dollars (driving up the value of the dollar on the market) and buy US bonds. (Some people are still buying German bonds at negative rates, but I admit I don't get it. I suppose they think that is a safer form of wealth than money deposited in a private bank.)

When the dollar goes higher, Americans can buy more imported products, but it is harder for American businesses to sell abroad. A lower dollar helps American businesses marketing around the world. So, lower rates are good for that. Also, lower rates make borrowing easier...which is good in the short term (so the US markets and presidents of both parties love it) but potentially (almost certainly) bad in the long run.

Yields are a different matter. They are more an indication of confidence in the US, I think? I'll let someone else comment on that.

I think ultra-low rates do fuel a market bubble. I hope the bubble lasts through the next election. Obama was a beneficiary of the housing bubble popping before the 2008 election. Bush didn't make the bubble; both parties allowed it to happen; the timing of the pop possibly affected the election, though. But, make no mistake, any bubble is bad if it gets too big. We had a major money supply bubble build up under Obama (Supported by McCain & Bush), and that has still not been undone.