PageRank has nothing to do with relevancy. It only has to do with link popularity, So links from off topic pages are worth the same as an off topic page assuming they have the same PR. However, keep in mind that this probably won't help your rankings since those links will have little value towards your page's ranking and PR has very little affect on ranking anymore. So basically those links won't do much of of anything for you SEO wise if they even do anything at all.
Do to obvious confusion between PageRank and a page's ranking I'm going to provide more information.
PageRank is a numerical representation of a page's link popularity. Not it's relevance for any given search term or anything else you may want to associate it with (i.e. reputation, etc). Any link that is not
nofollow, regardless of the location of the link or the content of the page it is on, will pass PR to any other page it links to also regardless of the location of the link or the content of the receiving page. This means all things being equal (identical PR, identical external links) a link from an unrelated page with a PR of 4 will be of equal value as a link from a related page with a PR of 4 when referring to PageRank and not a page's ranking.
Now if you are concerned about your page's ranking then relevancy of the link will be a factor. So, using the same example above, the link from the PR4 page that is relevant to yours will carry much more weight then the unrelated page when it comes to determining your page's ranking.
So if your goal is to increase your PageRank, then any link will help you. This includes links from unrelated pages.
If your goal is to improve the ranking of your pages then these unrelated links will not benefit you. Yes, it will increase your PR, but PR is just one of many ranking factors and it seems that nowadays it's not a very important one.
PageRank is a published formula. The only portion of it that may have changed is the dampening factor. But this otherwise clearly explains how PR works and that it is only a reflection of link popularity and nothing else. Remember, this is the PageRank formula, not Google ranking algorithm.