I'm still w*rking full time but have two teens with college on the horizon. I model/manage the financial impact of this by just pulling it all out of the retirement & net worth calculations -- both the saved assets designated for college and the college expense obligation. I treat future college costs as my first obligated dollars and nothing is available for the retirement/net worth pile if that's not funded.
I find it simplifies both my modeling and my sleep to clearly drive a wedge between college planning and retirement planning.
My $0.02.
I don't include 529 money when I use firecalc - but I do when I use Quicken Lifetime planner. My goal is to fund in-state public schools and I've budgeted $100k per kid *above* the nominal spending (which already includes their health insurance, food, etc.). To be conservative, I don't have a spending drop when they are launched and independent... but I suspect that budget excess will be consumed by travel.