If your Avy has a 12k tow rating, then it has the 8.1L and 4.10 rear axle like my Suburban. Any Expedition is not going to handle the weight like your current vehicle. The only thing that will replace your tow capabilities and current garage length requirements are a reg cab 2500 truck or possibly a crew cab with short bed.
If you want a new SUV for daily driver, then I would get the Expy and keep the Avy outside as a dedicated tow vehicle. If you don't trailer anywhere else except back and forth to the seasonal lot, then I agree just hire someone 2x/year for that job and buy whatever you want.
This is exactly why I haven't been in a hurry to replace my Burb.....
PS if you decide to sell the Avy, post a link here to where it's listed...even though this isn't a "for sale" site, these vehicles are getting hard to find and it's almost a public service for folks looking for a HD SUV for towing.