Inna, I just compared a 6 inch woofer on a two way, to headphones, to 12 inch woofer in the listening room. Bass is bass; naturally the 6 inch woofer on the two way in the bed room came up short, but so are the quality of the electronics. The headphones were better than the two way in regard to bass.
Since I've never had anything other than a 12 inch woofer, I can't comment on that, but a 12 inch woofer "feels" right; in other words I'm accustomed to "feeling" the bass. In regard to economics, an 8 inch woofer could cost more, and be of a higher quality than a 12 inch woofer, but the biggest cost increase is the cabinet; and that's more of a reflection of the manufacturers cost increase versus profit.
Without actually knowing the difference, I think you should audition the difference in your listening room. The enjoyment of music is very important to me; it's my main enjoyment, and when the economic factor is within reason, the only thing left is discovery. Audition speakers with 12 inch woofers in your listening room; in your listening room is a must because 12 inch woofers cause resonance problems.
Enjoy the music.
