Hi Bruce,
If it were me the sentimental value would win out even if I had to keep it until I were a very old man before I got time to bring back the memories.
Anyway you are asking about value, in the last couple of years I have purchased two similar bikes from the US, one was a 74.5 Penton 250, the one that is a "more desirable" than the one you have, it came from a member of the Penton owners club and although it was not bright and shiny it was ready to race and race it I did for two years and it never let me down, only thing I did was new tubes and tyres and usual servicing, that bike cost me about $2250 US plus $250 internal transport in the US and about $1000 to get it over the ocean and some GST, I forget the exact figures (I'm a married man and I don't keep records for obvious reasons
) and that was a good clean running and ready to race bike. The second bike was a 77 KTM 250, paid $2100 US for that and about the same transport and shipping and GST as above, it was not ready to race but was all there and was running it just had never had anything done do it in the last 25 years so every seal needed replacing and there was a bit of general deterioration/surface rust and while it was apart it got (and is still getting) a freshen up.
So you can see that assembled and running bikes from okay to really good condition cost about $3500 landed at your front door in the eastern States, and dare I say it, the 74.5 Penton 250 and 77 KTM 250 are perhaps more desirable than what you have. And here in Australia that desirability is perhaps in some part because of our pre-75 and pre-78 race classes.
And when I was looking for those two bikes I came across plenty of "basket cases" ranging from your basket case which seems to be pretty well everything included right through to a box of bits and pieces, and those were from about $1200 US down to $500 US, and the shipping costs would not have been much different, so perhaps you can see why I purchased running bikes.
So, in my opinion your bike is worth what somebody would have to pay for the same thing from the US plus a little bit extra for the fact that they can see it before they buy it, so that puts its value at say $2000 up to $2300 But then you have to take into account what it would cost to get the frame back to standard, so you would perhaps knock $300-$500 off so you get down to about $1500-$1800.
And that sort of valuation is very different to the prices that are paid for absolutely perfect restorations, bikes that are nut and bolt correct every spoke every nipple every bolt every nut as it was from the factory, even with the correct paint type and colour and with tyres from "back in the day", to the right collector those bikes can demand the sort of money that has been mentioned above but you could probably count the number of them on your fingers.
