Re: how much difference in tone does the wood make.
It really depends on how anyone percieves it as most have set mindsets of what makes a guitar tick. In a book by Bob Benedetto, he made an archtop out of pine and low grade maple for clinics in order to show that you do not need superior tonewoods to make a superior instrument. What is interesting however, is that some people might think that the pine archtop guitar sounds good because it was made by Bob Benedetto. If they did not know it was made by him, they might percieve it to be somewhat inferior in sound.
In any case, wood can affect the sound and I really think it can be related to the density of the wood and it's rigidity. For example, we can take the neck of the guitar, and look at it as a cantilever. The more rigid the cantilever, the more high frequencies are retained. The more the cantilever vibrates and the less rigid it is, those frequencies tend to be lost. So compare a maple neck to a mahogany neck, the maple neck being more rigid will make for a brigter sounding guitar. Also, the fingerboard wood affects the rigidity of the neck as it is glued to the neck. Ebony fingerboards tend to make guitars sound brigther.
Although the wood of the guitar can make a world of difference in sound, so can many other things: Headstock angle, thickness of the wood, tuners, hardware, even the nut material. Hope this was somewhat helpful.