Voodoo: its funny you should say, but I had some frieky good luck. If you look at most of the oscars sold at petcos (at least mine) now, they all have the elongated body shape. Mine has the natural full body shape. I had no idea of the difference at the time that I bought it.
I find it hard to judge a particular pellet. With the variety that I feed the fish, I don't think that there would be much of a difference between it and hikari cichlid gold. However, my picky dempsey goes nuts for NLS. The 1 time that I'll see it aggressive now is when new life spectrum pellets hit the water. The silver dollars go for it, the oscar goes for it, the crayfish goes for it, the midas goes for it, the danios go for it. So the fish universally like it, and it seems to be more cost efficient than hikari cichlid gold.
Sump: Also funny you should note about the digging...my dempsey started digging a bit around "it's" cave (reason for the "" is that the fish don't really fight for territory)
I bought the silver dollars at 3". At most, they've grown 1-1.5 inches. They were purchased at the same time as the cichlids. So as you can see, the growth is SLOW. They aren't very active and dont' really move all that much. They aren't really wary of the cichlids. The cichlids used to take shots at the silver dollars to try to hold territory. A few scales would fly, the silver dollars would swim away, and a few minutes later, would swim back. Now the fish don't seem to care too much about territory.
I believe that they would be more active and less skittish if the group was significantly larger (talking at least 6). That being said though, silver dollars can be EXTREMELY fast and destructive scared. Probably not capable of breaking a heater, but lets go back to max size. I've read sources that say max size is between 8 and 10". If you had one that attained a size of 10", it could probably break a filter intake, and possible a heater.
Durability: They've done fine in my tank, but my fish are not very persistant. Any aggression is a 1 shot deal that is over in 1 "charge". My silver dollar's carelessness of not running when attacked makes me wonder if they could last with true aggressors like red devils, trimacs, guapote, etc.
Overall: If you have a big tank, it would probably be cool to get 6-10 of them as see how they do. However, I think danios & barbs do better as dither fish because they seem to swim more, reguardless of how many of them there are.
each of them had ~1" per month.