I tend to agree with you on this. I never really buy "booster pack" DLC, purely because its content (like new weapons, maps and characters) feels really light for the price.
It's like buying a cake, and getting the icing afterwards as an "added extra" I have to pay more for.
Luckily though, Gears 3, as it is, holds up perfectly well with the content it came with; so I'm not feeling like I'm missing out on too much at this point. I am excited to see what else is coming, though.