Is it good to get high pr links from unrelated sites?

Yes! While the link juice of related sites is valuable, I got a few sites to position 1 by purchasing front page links on high PR sites that we're not in my field whatsoever, just targeted my keywords!

-Collins P

Really it just depends, how old is the site? If the site is a bit older you don't really have to worry, if it's relatively new (ive found under 6months old or so) you can get sandboxed quite easily.

-Collins P

In my opinion I think that your site would be fine and the sandbox is nothing to worry about. In my experience the sandbox only occurs if you do something stupid like blast 10K links from the same type of platform to your website (blog commenting, forums, etc..)

If most of your main traffic is generated by SEO then I recommend to focus your link building from related sites + articles. Because you have a highly specific niche you could easily start a article marketing campaign that grabs in all the long-tails you are trying to rank for and direct them towards your website.

When it comes to buying links you should really ask yourself could you better spend that money buying banner spots from a related website. Try to kill two birds with one stone: link building and traffic generation. Try and find some blogs that are related to your niche as well as forums. By doing this you are building backlinks as well as generating targeted traffic.

Tip: Whatever you end up doing make sure you have the anchor text be your main keyword. It goes a long way.

My .02

Personally if it were me I would get a good article spinner and then submit spun versions of the article to directories every day. A good article spun to 70% uniqueness would get you around 100 - 150 unique articles at the least. It might take an hour to spin the article but the benefits are obvious. I would do 5 a day that way the published dates aren't all the same. I would also use different "ghost names" in the author box so as not to arise suspicion with the big G.

I think a good general rule is that although in niche links are probably better (maybe, but probably not for SEO, but they can at least lead to more traffic) they are not so much better under any circumstance to be worth the huge extra effort.

I have not seen that related vs unrelated really makes a difference. Nor does PR really seem to make a difference either although I have noticed that higher PR links does get Google to crawl your site more often. Definitely.