Yeah. If she's really wants a ML, definitely wait for the 2012's to come out. This way you can get a much better deal on a <2012 ML if the 2012's don't meet expectations. Usually love picking up last year run models when the new models come out. Typically savings of at least an extra $5K-$10K more than what you can get regularly.
Though this could back fire on you if she then wants only a 2012. Hard to get good deals on 1st year run models (typically for most people). But at least you'd have a first year run model. Have to weigh what you really want. To spend money on newer technology or get the most out of your money.
To convince her to wait, you can always point out that you've already spent quite a bit on the 2001 325ci. It should last long enough for the wait. Afterall, what else can break, you've practically fixed it all (my mentality on our 2004 325ci that we've had repaired numerous times around 70K miles too). Kind of a waste to spend the money on the repairs and then just get rid of it.
In regards to reliability between the ML and the X5. Think they are pretty similar.
X5 definitely has a nicer drive. Maybe 3rd row seats (that most will find a waste of money) can be convincing argument for the X5. It was for me
