I've sometimes wondered the same thing. I also wonder what it would be like to have such and such a part on my Sport II. Then I remember what I did with my Mossberg 500. I learned my lesson with that. As such, I am extremely hesitant to go down that road with an AR, especially since ARs have what seems like an infinite list of options compared to the Mossberg. I've also learned with the Mossberg that I don't like having unused parts sit around. In the end I took my Mossberg pretty much back to stock, except I switched the plastic furniture for wood.

I also like the basic M4 look that the Sport II has. It's got nice, clean lines. I'm perfectly happy with the standard A2 style parts that the Sport II has, that everybody seems to switch out. I looked at more expensive rifles, but in the end the Sport II does everything they do for a lot less. Even though the Sport doesn't have a heatshield in the handguard, I haven't found that to be a problem. Now that it's cold out, if I shoot it, I like the added warmth.

If I ever get to the point where I want to start modifying the Sport, I'll just build another AR. That's something I've always wanted to do anyway. Until then, the standard Sport II satisfies all my AR desires.