On the ALMS vs Grand Am debate, this is how I see it.
DP is a 10 year old design, meant for close racing. Fans like close racing. Prototypes are cutting edge with modern technology, but that inovation leaves some teams in the dust, and makes for smaller fields as it is more difficult to be competetive.
In GAGT you have tube framed GT cars, with little/nothing to do with their roadcar counterparts minus the (highly modified) engine, with a BOP to artificially equal the cars, with varying levels of sucess. In ALMS GT you have production based cars, with production chassis and engine blocks, and are fitted with technology relevant to roadcars. Again, it is more difficult to be competetive, but it has also produced arguably the best racing in the last 10 years or so.
Personally, I prefer the genuine racing and relevant technologies of ALMS, after all, the point of racing is to demonstrate why your cars are better, and to do that you need real technology.
However, I can understand why some would prefer the close (although artificial) racing of Grand Am. Watching 10 cars battle for the lead is more exciting than watching 3 cars battle for the lead, and that is what Grand Am has to offer that makes it attractive for the casual fan.
Edit: And like it or not, the merger has killed any hopes of LMP racers in North America. Since Nascar bought ALMS, the LMPs would be slower down, making them rather pointless since the point of a racecar is to go as fast as possible. Why would a team spend money on a car that will be irrelivent next year? That is why ALMS testing had so few cars.