Worth getting when you don't need it?

CBU2004

So I started with a Vanquis card a few year back, then applied for ASDA cashback CC and got it, had it few years now, got way more than enough credit, love the cashback, pay off balance each month.

So pretty set with CC's I guess.
I ask however, because since I got my credit up, got a few store cards, some accounts with things like ACE and ShopDirect etc... I keep getting offers left, right and center through the post.

I get them mainly from Barclays offering a CC - should I just apply because, it's worth having an extra one right? Also they would stop sending letters lol.

I know I will never use it unless it's an emergency...

What you guys think?
Can it only help my credit to have more cards? Will it hurt it in any way?

Cheers