Via NASAwatch - NASA administrator Griffin replies to the American Astronomical Societies' Six Questions On NASA Priorities and Processes
Read it.
Interesting, tempered, with interesting conceptual holes.
1) the "mission balance" is not just different size missions, it is also different sub-fields.
If there is any desire for a long term broad space science program, then there needs to be a balance between sub-fields, not just mission classes.
2) there is serious disconnect on the "workforce crisis".
There is a very frustrating "MBA mentality" which seems to think that science expertise is fungible and can be purchased off-shelf. It isn't and it can't be - it takes 5-10 years to build expertise and a significant trained workforce (with one exception, if you can persuade everybody to drop everything and do a one-time push on something important - a la Manhattan Project).
So if you disband across a field, even for a couple of years, then you take a decade to recover.
People will stick around for a year to see if funding comes back, much more than that and you see an exodus - to finance, computing firms, plumbing etc. You permanently lose what you spent a lot of money building up.