Thank you, both of you^ I'm starting to think it was a good buy even if I can't restore it. It's nice to have around, it glows in silver, smoke or gold depending on the light. It has more life than any piece of clothing I owned before.
I've searched for information and I think I'll settle for "reasonable restoration", something between the preservation done for museum pieces and the more drastic changes sometimes made to a wearable.
I'll try to preserve the overall design and shape because I think that's more important than the beading when it comes to design integrity. It's tempting to cut it up to get hold of extra beads and fabric and make it a bit smaller but I won't do that even if it would make the dress less fragile...
I think it might be possible to add beads that aren't a precise match, esp. the black ones, or just leave it with some beads missing. I think the shape and pattern is more important than detail.
Would like to hire a pro for this but I can't afford that.
Not sure if it will ever go out dancing again because it's sooo fragile but it would be nice to see it on a person or on a hanger at least once...
If anyone knows an online shop for antique beads, please let me know

Eller om ni bor i Sverige och känner till en fysisk butik ; )