Let me tell you why she is running THIS YEAR:
1) Why wait, when you can move in now? Hillary sees President Bush as a knock-off of his father, who she has fond memories of ousting from the White House. She sees the war in Iraq as 43's Vietnam quagmire, and believes he is beatable.
2) She can't wait until 2008. She'll be four years older, four years fuglier, and four years fatter. The internet blogs will completely police the mainstream media, forcing more of the truth to come out than ever before. This year is just a taste of the power of the web.
3) She can't wait until 2008! Hillary doesn't want to wait, she wants to rule the World now. She doesn't want to have to run for re-election of her Senate seat, Rudy would kill her and ruin her political career. She needs to move on, and up, ASAP. She knows that she won't have anywhere near the backroom string pulling ability if her AND Bill are not in any position of power, and the MacAuliffe DNC-Clinton machine will be fully disassembled if Kerry gets crushed in November and takes House/Senate/Governor seats down with him.
Now, if you STILL think she's running in 2008: Don't hide your head in the sand like an Ostrich thinking that she's not running until 2008, so we don't need to worry about her yet. EVEN if she's not running this year, it's better to slay the beast before it reaches maturity.
I agree with your reasons. I've had a bet with a friend since the start of this year that no matter who got the nomination, Hillary would be the Dem candidate on election day.