dealer and have them do a deep dive mechanical analysis to see what, if any, of the systems need maintenance or update?

As an aside - our current 2 Toyotas (2011 Avalon with 155K and 2006 Tacoma with 54K) are running great. But I've had the same thought about updating our Avalon for the same reasons you list for long, extended cross-country roadtrips. I think for more local trips (within 1,000 miles) I would be fine with our current Avalon, but for cross-country I'd get a rental and put the long mileage on that.