First off, they are changing to new smart cards, and some of the older receivers are not being upgraded for the new cards.
Second, since you are a long-term customer, you should be able to get a good deal. They will replace the 500O with current equivalent without charge, but if you want to upgrade, then the usual Dish'N'ItUp terms apply - which, again, are better for long-term customers.
When you add an HD receiver and HD channels ($10 a month for the channels), then you should get a free install of a Dish 1000+ (yes, the Raleigh HD locals are on 118).
By the way, getting a DVR makes as much or maybe even more difference in watching TV than HD. So, you should consider an HD-DVR, models 612, 622, or 722.