We've got two, or maybe three tractors which are not going to leave, period.  That has nothing to do with anything.  If I tried to list them on the net worth with $1,000,000 of value I don't think anyone would buy into that.  If you can get away with booking your D17 at that value it most be something really special, or else you deal with pretty sloppy accountants and bankers. 

Good accounting of business costs and profits works for anyone.  If you call that B.S. I don't understand your reasoning there, and I would still maintain that such an aversion to accurate accounting is a recipe for possible financial disaster.   Whether or not you should 'squeeze the last dollar out' is a decision which can be made on a case by case basis, but how does one make rational decisions if he is  not accurately aware of what he is spending and making?

Staying on the machinery aspect....when did they quit making the D17?   I didn't know it made it clear till '68.   I would have figured the one-seventy was out by then.  Don't really know A-C all that well.