Whats the difference between silver plated and gold plated mouthpiece (excluding price)

Never heard of such a thing as silver-plated mouthpiece, maybe you're talking about silver finish (regular mouthpieces)?
Then it's not plating, but anyway thats not the point.

Gold-plating is known for giving a slightly darker tone by eliminating high overtones. I also find that it's softer on the lips, so more comfortable.

And to answer the title question, I use a Yamaha Alain Trudel Signature (which does have a gold-plated rim and cup) that I just bought a week ago after a month of trying various models.

Oh and I did compare the Alain Trudel Replica (which is silver finish) and the gold-plated one, and, I found that there is a difference. It's not a huge difference, but there is one, as I said, mainly in the comfort.

I've always felt that gold mpcs warmed up against my lips just a wee bit faster, and some find it simply more comfortable. Most players find it has little to no difference in the sound. Some players have allergic reactions to the silver plating on mouthpieces and switch to gold for that reason also.
to answer the question in the post title..
my mouthpieces..
alto trombone.. bach 4C (silver) (though pondering switching to a 7C)
small tenor.. doug elliott XT103 lexan rim with C cup and C3 shank
large tenor.... doug elliott XT103 lexan rim with G cup and a G9 Shank
bass trombone .. Ferguson L (silver)

Most all mouthpieces are plated. they are made of brass then often plated with copper and then silver or gold.

I have understood that Gold will warm up faster on your lips. Gold will give you more of a 'wet' feeling, and it is said godl gives a smoother/softer feeling sound.

Silver will give you more of a bite and it better for dry lip playing.

I play on gold rims and I play on nickle rims (which is not the same as silver although it is related. Gold is pretty and feels softer. I do not plate the inside cup of my mouthpiece yet I still get a great sonorous tone.

Gold plated mouthpieces have always felt smoother for me and seemed to float on my face. I currently have decided to get a custom euphonium mouthpiece made, but here is what I have been using lately.

Trombone-Silver King 6 1/2 AL, or Gold Denis Wick 6BL
Euphonium-Silver DEG Brian Bowman BB1