Vanfan: I made a typical and simple $100,000 mistake in 2000 and 2001 that very nearly cost our son his education.
Perhaps the question whether to stay in an UTMA or go into a 529, is immaterial, if you are not properly allocated in your investments and risk tolerance.
I sold my mother's (then 82) mutual funds in 2000, on the premise she doesn't need the market risk. I neglected to sell my son's (then HS junior) aggressive and growth MF on the premise that he had another 50 years to recover any market loss, and I got greedy. In ass-sight, I realize that his "retirement date" was really less than 1 year away (fall college applications, January FAFSA. and spring acceptances).
If you also remember 2000 and 2001, the MF's had a lot of capital gains. The UGMA were fully invested, and when his tax bill came, I had no choice but to sell some of his assets, to pay Sam. I assure you that selling assets in early 2002 was necessay but not easy. I realized my risk-horizon, error and sold more assets to rebalance the portfolio into lower risk "incollege" in our 529. If you have read some of my earlier posts, then you will read that I was really ticked to see the most conservative portfolio in the 529 lost money - and I bee'd lined to our Sec of Treasury to complain.
I don't know your situation or how the money is invested, But IF there was another 9/11, Bush does something really crazy, you lose an income, China no longer buys our debt, drought in the Midwest, earthquake in S.Cal ...
Our son's UGMA portfolio is now successful primarily because of a scary amount of low cost student loans and a market recovery.