Expert opinions please: buying expired domains using DropDay, SnapNames, GoDaddy etc.

Hello all! First-time post and, if I could make my text green, it would be more than appropriate!!

I can't even remember how I found this great forum. But I did read the thread "What paid service could you not do without?" and found that somebody mentioned DropDay and buying domains via NameJet, SnapNames, GoDaddy Auctions etc.

Now I am hooked on the idea of buying about-to-expire domains. But I have to learn more before I waste too much money (this last-minute buying thing is so much fun!). I have already spent maybe $200 on three domains -- so you can see that I have put the cart before the horse here and it's time to stop spending and start reading.

I'm not afraid to invest in my online business and I think being too cheap is a bad practice, but I want to make sure the investment is worthwhile.

1) What exactly are you buying?

I guess you are buying the domain name for sure, but the interesting part is, DropDay allows sorting by Daily Traffic, Google PR, Alexa ranking etc.

So when you buy the domain, are you also buying the benefit of that link juice as well? Or will those links be lost if you don't replace the site like-for-like on a new host?

Is there anything special I need to do to preserve the page rank of that newly acquired domain?

2) Where is the value?

I can totally see the worth in buying a domain with page rank and redirecting it to a related project. For example, I have several party games websites, and if I could buy a party-named domain like party-scene.info which has page rank and redirect it, then that makes a lot of sense.

It would also explain why some of the older domains with tons of links and a high PR go for thousands in the auctions. But I'd like to hear from people here with experience and knowledge in this topic before I get too involved.

A domain related to one of my sites went for about $800 and I backed out because, while the daily traffic of 600 per day was a bargain at that price, it wouldn't be a bargain if I would lose that traffic by simply redirecting the new domain name to my existing web content creation site, rather than building a new site at that domain and hosting it.

Thanks so much in advance. I hope to be useful to others and pay it forward also; I'm not this green in other areas!

Regards, Ashley