Congrats on the RCA plasma. I just calibrated one of these on Tuesday and was surprised to find that it was, as best I could tell, electronically identical to the Pioneer Elite plasmas that I've calibrated -- and the Elites carry a $17,000 MSRP, though they more typically sell for around $10,000.
On the choice of HD sources, this is a tough question to answer definitively, but you'd be well-served spending an afternoon reading through the STL threads for the past couple of months. There's been a LOT of discussion on this subject here.
As far as image quality between Charter and DirecTV, I have DirecTV at home but based on what I have seen on customer calls, there's not a substantial difference between DTV and Charter. That might change over time, but for now the quality is very good regardless of which way you go.
The real issue, it seems, is quantity, and Charter seems to be doing its level best to leave customers to completely guess what its plans are for additional programming. It is supposed to begin charging for its HD package in the New Year, but I suspect that any attempt to do that without matching the DISH and DirecTV offering is going to result in defections.
Personally, I think you should just bite the bullet and buy a full-fledged DirecTV HD receiver and begin to really enjoy the investment you've made in your new display. When the DirecTivo HD box comes along, you can sell the old DTV HD box on eBay or by posting here. Maybe you lose $100 or $150 in the interim, but that cost is likely to be spread across at least 6 months.
With the impending approval of the DirecTV sale to News Corp. and the fact that News Corp. already has a relationship with a different PVR manufacturer, I suspect that the delivery of DirecTivo will get bogged down further.
Bear in mind, that's just my opinion, based on my own reading of what's happening with TiVo and DirecTV.