Yes, we should, and the reputation required should be 1, at least for papers from the arXiv. Since ultimately every arXiv paper is to be imported anyway there need not be an upvoting system for arXiv contributions.
In fact, we should do more.
Indeed, I find myself regularly writing requests for importing arXiv papers that are referenced in discussions.
It would be very desirable to automatize this so that references to arXiv papers in contributions elsewhere automatically lead to the creation of a page for refereeing it (if it does not yet exist). The link in the original contribution could then go to the review page rather than directly to the arXiv page, and there should be a link back from the review page to every contribution (including comments) that link to it. While this may be some work to implement it would be very useful. (At present such cross-references have to be created by hand, which is a chore, so I do it only very selectively, and therefore find myself frequently searching the pages for references I have seen but not noted.)