If you love Siamese cats so much, I see no reason for you not to get another one to love.
Have you gotten your other cats from breeders or from rescues?
I think I must be lucky with getting my Siamese cats, they have both been healthy so far with only the problem of getting rid of fleas and worms when I first got them.
My cat Milly does have a high food drive and will tend to overeat until she throws up but we monitor her food intake and don't free feed her so she doesn't throw up very often now.
I know Siamese cats are special, one option you may want to try is to find a mix like a Snowshoe that has many of the Siamese traits with less inbreeding.
Have you looked at the cats at Siamese Rescue?
I'm sure you will be able to find a new kitty to love there.
http://www.siameserescue.org/