Each time November comes round, I contemplate NaNoWriMo, but fortunately common sense has always prevailed. Working full-time and having a long commute, there is just no way I could keep up 1667 words a day.
My average daily output on Moving a Mountain was 719. Maximum written on any one day was 2384. (I'm not counting the 5480 words written on the last day during the final sprint for the end, because only the first half were kept. The rest were very heavily rewritten.)
You can see from those figures that the reason for my lousy output is not that I write very few words per session, but that I'll go for weeks without adding a word to whatever project is the W supposedly IP.
Once Moving a Mountain was at the revision stage, I tried working on two projects at once. I did some initial planning on the magic college novel and I poked at A Necessary Evil (50,000 words already written some years ago). But apart from doing a little bit of revision of the early chapters and, in November (spurred on by the NaNoWriMo frenzy), adding a few thousand new words, I wasn't really writing at all until I spotted novel_in_90.
Since then, I have written consistently for at least 5 days every week and my current daily average is 924[*].
Right now life is slightly on the stressful side of average, so if I can keep up this level of progress now, I should be able to do it most of the time. And this rate of output is enough to produce a novel a year (including time for a revision pass), even while working the day job. If -- big "if" -- I ever sell a novel and get actual money for it, I can reduce my teaching hours a little to give me more time for the writing.
A target of 750 words per day is exactly right for me.
In the meantime, every time I think of the novel and how unoriginal it is, I just beat my internal editor over the head with a wet fish and dance round her chanting:
iTs just the shitty furst draught, yoo can allways go back and change ti later. Gofor it!!!!
Besides, it doesn't matter if this sucks because it's just a self-indulgent thing you're doing for practice so that you can write the "miner's strike with dwarfs" story. When you've honed your skills on this, you'll be able to write something really good.
There is no idea so old and hackneyed that a good writer can't make a good story out of it.
[*] My official novel_in_90 average is the slightly lower 686, but I just can't write every day with my current workload, so I have slightly modified the goals.