I am considering buying a link on a home page that is just about as related as you can get to my site. It is top 10 for very competitive term in G but nowhere to be seen in Y! or msn for the same term. Strange I know, most people have the opposite problem. This will help me significantly won't it, considering I am up there in Y and MSN but nowhere in G? I'm sure it will, justlooking for some reassurance from the more knowledgeable amongst us
Well, the more related, top authority links you get the better. If you're stuck in the sandbox, you need to continue to acquire these types of links before you'll start to see yourself ranking nicely for your keyword terms. So, should you get it? Yes. Will it help you significantly? No. It won't help significantly, in the sense that their is one "magic link" to get out of the sandbox, if indeed you are in it. But, as you said, it's as related a link as you can get, so that means that not only is it a good link for link building purposes, you'll also be driving related visitors to your site.
I am not in the sandbox (thankfully) and it is one of the biggest authorities in the field, not sure wht my expectations are really, hope i'm not dissapointed though
About a year ago one of my websites (a free geocities site) got a link from a pr8 related authority site , shortly after that it went from page 17 to page 1 on Google for a vey competitive 2 word key phrase that brought up over 40,000,000 results and the pr went fom 3 to 6. So who knows what will happen.