Suppose your home or index page doesn't receive a reasonably good ranking in a particular engine for certain keywords or keyphrases, but lets say 4 or 5 pages deep in your site, the spider tends to like better and thus rank them better?

It doesn't much matter where a surfer enters your site as long as they can navigate and find the information they seek. Every page should be designed to be "user friendly".

If you concentrated on just getting everyone to the index or home page only, you would end up trying to optimize one page for tons of relevent keywords and keyphrases. This doesn't work well. Each page should be optimized for 3 or 4 keywords or keyphrases. This number can vary greatly, but basically, you don't want to overload one page for many keywords and keyphrases.