Actually most ideas are so terrible that I hope they don't read these forums at all.
This is very true. The suggestion thread is full of horrible ideas that can not realistically be implemented or would not be worth the effort to implement. Ideas that have not been thought through or just plonked online without even giving it the slightest scrutiny. Just reading that thread embarrasses me sometimes...
So no, Bethesda doesn't look at the suggestion thread in all seriousness - it's not worth the money to have someone wade through that giant pile of dung to get one or two mediocre ideas out of there.
But yes, they do read these forums, they pop in from time to time, see what the general sentiment is, what threads are popular, you know. They have a community manager whom they can talk to for that kind of stuff.