Strange question

First off I hope this is in the right section here

With vBulletin you can change the skin for each section of your forum.
If you were to use the same skin, but just alter the header info for each sub section of your forum, would that have diverse effects on google etc.

I use the vBulletin Seo skin, just altered a bit here and there.

So if someone was to enter the Auto Trader section of my forum and the header changed from The Spain Forum to Auto Trader Spain, would that add more relevance to the forum category or have I been on the sangria again too much and it would be too much time and effort for results accomplished or just upset Google even more

I know all the work involved and all you will accomplish is to change the H1 headers, which in theory would add more relevance to the forum category

Any ideas?

Changes in the skin itself from one forum to another will not likely have much impact. But, yes, customizing the header "text" to match the content for each forum better can be beneficial.