Thanks, ive tried posting comments on relevent sites with PR and this seems to be helping, it can also be done with a minimal of cost.
I think it is worth it provided the site is clean (eg: not spammy) and that the link is in plain sight (since you want traffic). If you only wanted page rank it wouldn't matter where the link is on the page with pr, but because you want traffic as well - make sure it's somewhere noticeable - ideally above the fold.