Actually, I think Hillary would do a "good job" in the same way her husband did a "good job."
1. She'd be following a very unpopular president, widely viewed as an idiot. That's useful for blaming a number of problems on the predecessor. Actually, she'd have an easier time with this than Bill Clinton did. George H. Bush still carried some dignity (deserved or not) whereas George W. Bush is pretty much widely panned by everyone. Note Romney's talk of how Bush mismanaged the war yesterday.
2. Like her husband she's very moderate and a true neoliberal. The market will appreciate that. Like Bill, she'll sell out the working class, the poor, and organized labor in a heartbeat to make money for the corporations. They aren't donating to her for her good looks - you know?
3. I don't think she'll unravel the defense establishment. In fact, she may boost it. The Army brass hates Rumsfeld and his crusade to create the "smalle, elite force." To many of them this Iraq War debacle is largely the doing of Rumsfeld's ridiculous ideology and the Bush administration's adoption of the Air Force's 50 year old lie. She could simply invest more in the Army and less on the AF and Navy and probably keep Defense spending about where it is or reduce it in other wasteful areas.
4. Foreign policy can only improve. The hatred of Bush did not begin with the Iraq War. He was arrogant from day 1 when he called up European leaders and told them they had to accept Turkey in the EU. Hillary won't make those impish mistakes. Again, she's basically replacing a team that went 0-11; she can only improve in this area.
5. Where I agree is on Iraq, the weak dollar, and Democrats.
Iraq is not going to be easy no matter what. Hillary won't find an acceptable solution that will improve her poll standings with Iraq. The dollar is very weak and to return it to strength will mean harming exports (but relief on imports such as oil). Lastly, I don't think Democrats will be as happy with "anything to win" attitude they had with Bill. I could be wrong though.
Hopefully she isn't the nominee...but we'll see.