Thanks everyone who has written urging me not to give up; not that I planned on giving up flying - just Dragonflying. But I am not giving up just yet. I have to try a new battery, check valve clearances, spark plugs, renew my battery connections etc.
If I do end up selling, she is newer now than when I bought her (as I have replaced lots of parts) so I know I will get my money back, but I must admit that I do love flying her and she'd be very hard to replace.
So, I am ambivalent, but ultimately I come down on the side of persevering and overcoming obstacles, so that I can enjoy pure flight.