I don't think they're practical. A halfway decent player can make out big time with them simply by manipulating the way points are distributed. Standin next to an objective and getting kills are an easy way to do this. Also its too easy to get lucky and earn low but lethal Streaks
I like scorestreaks. Sure people can exploit the system but atleast now people have some kind of incentive to play the objective. The only time where the scorestreeak system doesn't work so well is TDM and FFA.
TDM isn't dying it is still the most played gamemode. It's weird though because in blops 2 sometimes a game of TDM goes so quickly that streaks aren't really needed and there are other times when the game moves so slowly and a couple of streaks would be nice just to make the game play a bit faster.