its worth doing - you dont need much of either- i suggest eating the shrooms just as you feel that dose give you the shivers
I think the two should be used on separate occasions if you can unless you have a great abundance of the two. It's really not necessary though but it doesn't hurt to try it.
Acid+Shrooms is great, I definitely recommend it. It's especially noticeable with smaller doses i.e. 1 hit and 1.5-2g cubensis. I've yet to take anything stronger than cubes with acid but when the cyans come up here I'm gonna take a massive amount of those with some nice acid. Gonna give my ego what-for!