You don't say if you are buying or selling. If selling, its worth probably more to you (you have more invested) than what you can ask or get for it.
If you are buying, its worth is based on what you want it for, what you might have to invest in it after you find out what is likely wrong with it (truth is someone wants to get rid of it for a reason), and how much of a risk you are willing to take.
I looked for years for a JD 1010. It was the first 4 cyl JD came out with, and it was in the body of the time-tested MT, 40, 420, 430 series of the 50's. Good 3pt, good tranny, good workhorse of a utility size tractor (I had a 420 for years). I would probably figure one would be worth about $3500, give or take $1k for condition and desire to keep it running. I sold my 420 two-cyl for $5900 two years ago. The 1010 isn't the vintage material that the 2-cyl is, IMO.
I agree with pfoxy, I think that the diesel 1010's started on diesel and stayed on diesel. Some of the old Farmalls, though, did do it the way you described. They had all the parts to run it on gas (magneto, spark plugs, etc.), but also an injection pump and injectors for diesel so that once it started, you switched it over. And of course lots of the old two-cylinder deere diesels (and many others such as vintage Cats) used small, seperate, gas-fired "pony motors" that not only cranked the main diesel engine but also warmed it up beforehand (from the engine and exhaust heat). Though it sounds crude, this system worked quite well, much better than early electric start systems (which became available on Deere diesels in the second part of the fifties).