To be honest PR is just a number. Although it is pretty overated, you can see this when you sell a PR1 or PR7 site with the price difference. Alexa and PR could be brought about as the same due to them not really meaning much. Just one is more overated then the other.
I've got a site that makes me $1,000 a month with 0 PR and a 4m alexa, but well targetted natural keywords. If you're a smart internet marketer, you'll know that both methods of ranking are flawed and if you follow them, you are doomed to failure.
Adsense pays the same for sites with PR0 as for PR10... So I think PR is not that important (of course, if Adsense is you primar income generator!)