Agree, all alt coins are shit coins to me. They don't offer anything new over BTC IMO.
There might be some small differences but they are too small for me to care about.
With that said I believe in a free market and welcome any competition to BTC.
I have mined and used several alt coins but I only believe BTC one day might be an alternative to the dollar.

I think you should add Monero. One of the few alt coins that add anything. (privacy)

I personally don't bet with any other currency than Bitcoin on your site. But I don't see any thing bad about adding more currencies.
It might be more administration for you but other than that it will only help your site to be more popular.