The reason that Sauron attacked Lothlorien but not Rivendell and seemed to pay more attention to Lothlorien was that he didn't have an effective force in the north after Angmar fell. Because Lorien was further south and closer to Mordor, not to mention that it was right next door to his secondary fortress Dol Guldor, it posed more of a risk to him and therfore he watched it closer than Rivendell.
When Elrond said that his eye was fixed on Rivendell it was because the one ring was there not for any other reason. He would've had spys in the north so he would know if Rivendell was preparing an assult on him so he could prepare if necessary, but it was to far from Rivendell to Mordor for it to be a big enough threat for him.
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His sword was long his lance was keen
His shining helm afar was seen
The countless stars of heavens field
Were mirrored in his silver shield
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