Would a cold air intake help a bit in the hp increase? (for my 2006 accord) by how much hp? would it affect the mileage?

I have been doing a bit of research lately, what about an acura rsx- type s vs. a 2006 civic si? I think I can find cheaper acura rsx-type s second hand. The one that is keeping me from buying the civic si (new ones) is that I read about its transmission problems, ie grinding 2nd gear and 3rd gear pop outs. Are they true? and if so, can they be remedied by your shop in case I buy them?

thanks