I agree with your point of view completely. I am not even finished with my first playthrough and it has already gotten to be predictable to me. Tha major thing that is missing for me to make my experience more fun is random battles and skirmishes while out in the Mojave wastes. I am tired and bored with Cazadors. In the beginning they were a challenge and very annoying, but now they are just plain annoying. I agree, the game has fallen off since FO3. I may not even finish the game. I will most likely start a very heavily modded FO3 game or play The Witcher ot may even play Oblivion as I have never actually played the game. I don't think I will bother finishing, who knows?
Why not just mod this game. The increased wasteland spawn brings a bit more randomness to the battles in New Vegas.
Personally I see wasteland encounters as a nice aside, but not really a major deterrent from playing.
I agree with the OP, the game overs many things I thought Fallout 3 was missing and it's only true detractor is the fixed encounters.