Upload & Sell: On
(I hesitate to refer to you as Mr. Hog as I believe he was a major character in an ancient TV show called "Dukes of Hazzard.")
Yours is a particularly difficult decision because the 1DIIn (and the 1DsII) may have been the finest DSLR Canon ever produced. I feel strongly that much of Canon's now challenged dominance came from the excellence of these cameras particularly when compared to the competition's offerings of that time.
I shot both the 1DIIn and the 1DsII for about 4 years. The IIn is capable of superb images. It's rugged, fast, and to my mind handles wonderfully. I'm still a working PJ and - particularly in sports - found the 1DIIn unable to deal with the woeful light I'm forced to shoot in. It just didn't have the ISO headroom to deal with truly dismal small town football fields.
You note that for you "it's now more of a serious leisure pastime . . ." I gather by this that you no longer "have to get the shot to keep your job." As Photon and Jefferson have sarcastically noted, just because there is a later, greater offering doesn't in anyway make older cameras obsolete.
In order to do my job I sold off both of my II series cameras and to fund a lightly used 1DIV. This is a very nice camera and offers several real improvements over the IIn.
1. Much higher useable ISO. - I regularly shoot at 25600. Yes, the files require a lot of work in post, but they are good enough for newspaper work.
2. Larger, nicer LCD. While this is good, it isn't that big of a deal for me as I don't do much "chimping' while working.
3. On the other hand it has Live View which I'm learning to use with lenses like the 24mm f/3.5L TSE in my other vocation as a landscape and "art" photographer.
4. A larger, faster buffer. Very useful in sports work.
5. Perhaps slightly better AF though I can't say this for certainty.
I have no doubt that the 1Dx is a better camera than the 1DIV. Full frame, stratospheric ISO capability, and higher thru put support that contention. It's also about 2x the price. (Nice used 1DIV ~$3500 USD, 1Dx ~$6800 USD.) Is it 2X as good as a 1DIV? Don't know as I've never touched one, though I doubt it.
I'd suggest you examine where, when, how you tend to shoot. Do you really need higher ISO? I found the 1DIIn good to about ISO 800 and 1600 in a shove. Do you need faster thru put? How valuable would full frame be to you?
Older glass (particularly L glass) never really goes bad (though it does pass beyond Canon's support window). Glass also tends to hold value far better than cameras. OTOH, Canon has dropped support for the 1DII, thus the 1DIIn can't be far behind though given how many 1DIIn's there are out in the wild, I suspect it will be quite awhile before they can't be repaired.
Frankly, you can keep shooting the 1DIIn for a long time and long glass is always seductive.
Like you I stay away from the crest of the wave - let others be Canon's beta testers! Because I'm still under deadlines, I try to stay about 1 generation back. The 1DIIn is now 3 behind. Maybe it is time to let go, but if you are like me, a perfectly functioning tool that I know intimately is VERY difficult to let go.
As I said in the beginning - you've got a real hard choice.
Good luck and no matter which way you go, it won't be a bad choice.