It's not exactly an unreasonable price...but I'm of the opinion that "classics" (aka. old ass games) don't age well because of the quickly advancing state of technology and the products offered by a service like this really don't justify the 5.99/9.99 price point.
They'll have to make some really solid choices regarding stock to find a large enough customer base. And by that I mean offer relatively recent games at the 9.99 price (NWN 1, Civ 3 gold, etc)...
I think devs/publishers need to really wrap their heads around the fact that games aren't like other forms of media (whose quality has stayed relatively stable through the years). There comes a point when they shouldn't expect to profit from old work and let it happily exist in the internet for free...if they want to make money, they can take the IP and create something new (or remake and update it).