from what I am reading and researching, the whole blown plug seems to be maybe a 1 to 5 % possibility. maybe greater on high mileage and lack of proper, dealer , skilled maintenance.
why go for the 90s when a good deal could be had at 2000-2002?
Why are you going for a Expedition ? if for the lady, does she need that much room? Is she hauling around 8 kids? Why are you passing on looking at explorers? they are usually awesome with little problems for a decently maintained unit in 2000-2001. Better in MPG... and more units sold, i.e more info IMO
So far, and I am only 2 months into being a expedition owner, but 17 years with 3 Explorers owner... the Gen 1 expeditions seem great... minus an over inflated blown plug press.
my 4.6 has nice , decent, and more than sufficient power.... that is, for driving around the city and highway, inclines, declines and all... from 2000 to 9000 elevation... no issues
towing, well I have not done that yet.
The key here is finding the GEM that you are searching for or something that is ok AND you feel comfortable with for a lower price factoring in your perceived risk or investment for maintenance / repair
If you are looking ... post up the links to the ads and let us factor in what we think....
I believe that that GEMs are out there for a nice and fair price... someone needs to liquidate a great vehicle and little hassle from a serious buyer with cash in hand. You are in upstate NY, well, forget buying anything from there... Unless it only costs you 2 squirts of piss...
search online, find 3 to 5 to 7 in a southern city you like, and take a vacation down south to buy it, and drive it home. If anything is more than 8 years old there in NY, forget it, they are so rusted and the rot is setting in unless they were under coated.
The market really has been in Texas for Ford SUVs so enjoy a weekend in South Padre and buy a SUV in Houston.... enjoy the drive north, stop in Nashville for a great time, great music, cold beer, and awesome BBQ. That extra 500 bucks of a trip will save you hassle and money in the long range. 15-20 year old TX SUVs are not rusted in the frame, lines, under carriage bolts, etc. (just dont wear your Yankee hat, OK?)
Hope this helps.... BTW, I have an explorer and expedition that are in awesome condition... I think you'd , er, she'd be happy with either (both rust free)

and you 2 would have a great, fun time with me and a once in a life time drive home across this incredible country !
Food for thought....