I knew a flute player back in college who had this happen to him as well. That being, that he bought a new modern flute and it basically rendered his old gold Haynes to be at best mediocre. Technology, especially with the advent of computers and sampling and so on, is frightening in how fast it enables innovation and correction of errors.
His wisest decision was to sell the old model (for a *lot* of money to some enthusiast) and just play the new one. I'd recommend the same thing in your case.
How very true about technology. Yes, the newer Cooper scale flutes are much better than the old pre-Deveau scale Haynes.
However, this flute has sentimental value to me as I've played it since I was 16 in High School ... so I'm holding onto it.
I have several friends (some professional flutists/teachers) that still play their "vintage" Haynes flutes.
I've always liked Haynes since I grew up in Mass. I went to look at a couple of custom made Haynes from the 40's and 50's recently as I wanted to swith back to closed hole, offset G. I left the shop empty handed as they were pretty anemic sounding instruments. The 1970's Muramatsu I tried was so much richer, even my Mateki sounded better.
Maybe someday I'll find one I like.