After reading thoroughly many threads on latest updates, algo changes and the traffic shaping and normalization theory, it seems Google algo has fixed the Link buying thing.
Different algo for different sites - Some sites are still ranking via paid links but almost all of them are either brands or may be sites in the upper bucket.
I bought 2 PR 6 links, no effect on traffic and rankings.
I am of strong opinion current Google algo has taken care of this link buying manipulation.