Yeh, I understand that, but 1/ my initial Q was whether had been approached or not, not his reaction 2/ I can half-agree with you whether he would have said yes or no, so will play angel's advocate: a/ while he would be playing 'second fiddle' to Roger Moore, if he had been in the movie he would have overshadowed Moore, just as Christopher Lee did. It's possible BL would have considered that it would be fun to play 'second fiddle' but still be the guy most people would watch, instead of Bond b/ to appear in a Bond film could have appealed to him. He was probably a Bond fan. Even just from a professional point of view, he would have studied the Bond films, just as he studied the other action films of the day. If I'm not mistaken (others can fill in on this) he grew up watching action movies in Hong Kong, as well as 'kung fu action comic books'/pulp fiction.
Just imagining his mind-set at that period: in HK of that time BL would sometimes appear unannounced on TV just for the fun of it. So let's assume the Bond producers approached him in 1972, when he was still somewhat relaxed and not the super pressures that would come later (again, I don't know when those super pressures started, but I would guess at the start of 1973). 'Hm,' he thought to himself, 'well, this could be fun to be in a Bond film. After all, I have fun just walking unannounced, unpaid on TV; why not do it for the fun of it?'
Finally, to be in a Bond film would still be something to add to his resume. Of course, one can argue that he didn't need that on his resume. But businesswise, it would be a good move. Bond fans who stilled weren't too acquainted with Bruce would see him in Bond. New fans would get their first look. To appear in a Bond film would be big publicity, at the minimum. I don't think it would tarnish his star. It would be like The Green Hornet. No one was looking at the Hornet, they were looking at Kato. Imagine Bruce being in the theatre watching 007 and Bruce. No one would be looking at Bond! That would be a big kick to Bruce.