Hi Shawn,
Not solely for its PR or age. If you first find a good domain for sale that you'd like to use for a website or blog, then factors such as age, history and current strengths can be taken into account.
If you'd be buying it just to redirect it to another domain, then there will be Zero Pre-existing SEO value if it's dormant (not hosting a site).
Put things like age and PR to one side, think of why you'd like the domain and how you could use it, then bring back factors such as age and history to determine if it's actually a good domain 'for you' and how much you'd be willing to pay based on it's strengths and its value to you.
There are always potential issues to consider when purchasing a domain; check out it's hosting history and who has owned it previously, look out for it being associated with poor quality or poor neighbourhood sites such as porn and evaluate it's own inbound links. Wayback Machine can help as well as registrar history.
There is a useful video for you to view here on SEOmoz, entitled "Age of Site and Old Links - Whiteboard Friday".
Hope that helps, Simon