Photograph the package and all the contents 
(with time/date stamps on the photos); do it at 
the post office even if possible.  Maybe the 
USPS claims office will accept the photographs 
(the represenative and you could sign off on 
them) instead of the original package (probably 
unlikely).

But in any case, having photographs will be 
useful in dealing with either the USPS claims or 
the seller.

As to deciding whether or not to keep the items, 
that choice is ultimately yours alone.

Although it's hard to place a figure on rare 
collectibles, try to imagine what you would pay 
had you seen those items on sale in their 
presently damaged condition ... come up with a 
reasonable number.  Compare that figure to what 
you actually paid and look at the difference.

If you believe that you would prefer to live 
with the damaged items (because of their rarity) 
and the relative amount of money you would be 
losing (original value - present personal 
value), then you should keep the items.  Since 
the seller agreed to compensate for the damage, 
you should e-mail her the photos and both of you 
should come to some agreement for reimbursement 
(if you feel bad about the seller fully 
refunding your money, then come up with a more 
reasonable number).  You'll probably at least 
get a little more back.

On the other hand, if you think these items (or 
similar ones) may one day, someday, pop up 
again, then it's probably better to pursue the 
insurance claim.  Don't forget about the photos, 
as they are your record in case there is a 
paperwork SNAFU.

If you want to pursue the insurance and ARE NOT 
READY TO GIVE UP THE ITEMS, you should forward 
the photos (or e-mail scans) to the seller.  I 
believe that it is actually the shipper (or in 
this case, the seller) who must file the 
insurance claim.  If they are armed with the 
photos, perhaps they can file the claim for you.