If it's burned on vegetable oil, the pan is definitely not ruined. If the pan's interior is the black satin coating that is intended to be seasoned, then there's no particular reason to remove the film unless you don't want vegetable oil traces in the seasoning (I don't like Lodge's seasoning for this reason. And it's sticky.) If, on the other hand, the pan's interior is light colored enamel and you find the oil residue unsightly or are concerned about trace amounts in whatever you will be cooking, the residue WILL remove with simple baking soda and elbow grease. Less elbow grease = more boiling. Trust me. I've been through this many times with my all-white LeC pans...
As far as the outsides of the dutch ovens and other things go, as long as you don't chip them and don't clean with abrasives, I think the difference between the black matte and the black onyx (shiny) pieces would be purely a matter of personal taste.
For the interiors, however, the black satin is designed to handle higher temperatures and so will functionally stand up better to searing, browning, that sort of thing. HOWEVER, the satin finish is also designed to develop a "patina," and so its appearance should not be expected to continue looking like new.
Another consideration for many people is that they seem to find it easier to judge doneness of their food against the lighter backdrop of the white or sand enamel finishes. I myself haven't found the dark finish to be a problem, but I haven't yet cooked my entire repertoire with it.
I am a new convert to the church of the Black Satin. I've read many people's complaints about this finish on their grill pans, and wanted to counterbalance all that negativity. Maybe it's something about the grill pans, but with me and the Black Satin finish, it's love at first bite.
For years, I've been using an older Le Creuset "silverstone" interior (nonstick) to cook eggs and similarly sticky things. It works very well and I'd always preferred it to anything else I'd ever tried, plus the silverstone is a very durable finish as long as you don't overheat the pan. The older LeC white enamel interiors I found required a huge amount of fat to be nonstick. No experience with the newer sandy interiors, however.
But now my eggs and I have found a new love--the black satin finish interiors. I just tried out my new LeC crepe pan (black matte with the black satin cooking surface) for the very first time, making fried eggs. I'd previously swiped a thin layer of lard on the pan and heated it smoking hot for a few minutes, then cooled the pan down a bit, wiped it off, added a pat of butter and then the eggs. Smooth as silk, they slid off the pan when they were done. I wiped the pan off and slowly heated up a _tomino piemontese_. The exterior of the cheese seemed to melt more slowly relative to the interior than when using plain cast iron or the silverstone, but maybe that's just my warped perception.
Yesterday I had fried up some eggs the same way on a Lodge griddle, which has received rather more seasoning than the brand spanking new crepe pan, and the eggs left behind noticeably more of themselves stuck to the griddle than my usual silverstone-fried eggs. And when I melt a _tomino_ in a Lodge pan, I have to boil the pan with water and baking soda or freeze it and scrape off the cheese afterwards with a metal spatula or something.
With the new crepe pan, the small amount of melted cheese sticking to the pan was easily wiped away with my hand, once the pan had cooled.
So... also considering that the black satin finish is designed to handle higher surface heat than the enamel, I have no qualms recommending the black satin finish over the regular enamel.
I wonder why so many people have issues with their grill pans, though. Maybe I'll have to get one and see if I can figure it out...