Yeah, 105 is good stuff. You won't go wrong with it. (Personally, I don't care for Tiagra very much, but that's just me.)
It sounds like you want to go from a triple to a double. Keep in mind that not only are you going to have to replace the crankset, but also the shifter. That's a couple hundred bucks more. If you can live with your triple, and the chainring is all that is worn out . . . just replace the ring. (Other than the chainring, how does one wear out a crank arm? Is it even possible?)