mobo with sli does it worth it???

[isifgr]

i like to adress an issue here i was thinking to move to sli... but as far as i can see sli does not have great performance(ex. 6600gt<6800gt or 800xl), second you have to pay a fortune to have 2x6800gt at least to see the difference. finally the new gf7xxxx or atiR520 are getting out and their performance is going to be 2x than todays cards... whats the point of sli???? is it worth to pay the extra money to get it?? is it going to be nessacery for the future gaming or are for people who want to spend $1000+ to have the extra 20% more performance?? is it worth then to buy a mobo with sli or to get a nf4 mobo without it??