I've also been trying to decide if it is worth it to contribute to a 529 plan. I still have some room in tax advantaged accounts, so the decision I face is between a 529 and tax deferred space. If the decision is between a 529 and taxable, I think it would be an easy choice to use a 529, with the major risk being the kid not going to college or any trade school.
I filled out a FAFSA to try and see what effect a substantial balance in a 529 account would have on aid available. It seems a little convoluted, and not clear what the value of the aid would be when the only benefit seems to be non-subsidized federal loans.
For my situation, the comparison that needs to be made is the state tax-advantage (my state is a tax parity state) gained, vs the value lost by having the 529 balance count as an asset of the account owner for FAFSA purposes. I'm still trying to get a reasonable estimate for the value of financial aid. The value of aid received from FAFSA will depend on your individual situation when the kiddos head off to school.
If no 529 is used, I think the best option is to cash flow expenses as they arise.