I wonder how some agents get their licenses...sheesh!!!!! Ok, you have A) a round diamond, B) a baguette on each side, C) a gold or platinum setting.
Let's say for arguments sake that your diamond is 1 carat valued at $7000, your baguettes are .10 carat each for a .20ctw combined, valued at $240 (estimated at a cost of $1200 per carat..what they go for at a retailer here), and then your setting weighs 5 or 6 grams of gold. Don't know what that goes for, but I just bought a setting at that gram weight and retail on it was $300. (although I paid less, but I am quoting retail..and of course your setting may have cost more/less depending on metal, stone quality, designer, etc.)
Ok, you've got $7000 + $240 + $300 = $7,540.00 total retail ring value to replace.
I'd say insure the whole ring. My ring at $10k cost us $70 dollars per year to insure through Country Companies (I have home & car thru them as well) Our deductible is $1000 (same as our homeowners)
2 baguettes and the metal are not going to drive your premium costs up enough for you to even feel it, but when you are filing a claim if the unthinkable ever happens, you will be so glad that you have that extra value insured.
Just so you know... my engagement solitaire was $60 dollars a year to insure at a value of $6900.00 and when we added the new stones for the wedding band to that, the premium only went up an additional $10 dollars when the total amount was insured at $10k.
Your agent is not seeing the forest through the trees. Have the jeweler give you an appraisal with a breakdown, i.e. specs of each stone, specs of metal and total retail replacement cost. That is what you give your agent. While my ring only cost us a total of $5200, the retail replacement is $10k. If I lose my ring 10 years from now, $5200 won't buy the same thing.
If you insure "retail replacement value" and lets say your ring has a replacement value of $7540, but you only paid say $5000 for the whole setup, you have $2500 worth of "wiggle room" to absorb the loss associated with diamond prices possibly rising, or to counter the loss incurred with the $1000 deductible.
Obviously if the value of diamonds rising significantly, I'd get your ring reappraised every 5 or more years, as the replacement value may increase, making it crucial to increase the amount on your policy.
Cheers!