Agreed; plus, unlike the situation in the "World's Finest" film, Lois didn't know Superman's secret identity. In fact, it was due to superman not being emotionally available for her that paved the way for Bruce to sweep her off her feet.
However, based on what we've seen in "MOS" and what Goyer said about plans regarding the future of Clark and Lois, unless things change, Clark and Lois will be shown being in a "real relationship", with Lois protecting his secret.
Lois would look bad if she still ended up responding to Bruce's romantic advances, and people are still kind of feeling on the edge with how Superman is going to be portrayed next to Batman.
Plus, I don't think it'd be a good idea for them to establish that Bruce and Lois were former lovers as well. I may be old fashioned, but I never think it's a good idea to have two friends/partners share the same lover. It's just a mess.
That's why I was impressed with what I saw in MOS because for all the crap that Snyder and Goyer has gotten from fans regarding MOS, they at least portrayed both Clark and Lois in classy matters that befitted their characters with respect and dignity imho.
Which is kind of why I hope they're going with an older batman simply because it helps lower down the chances that they'll go down a lover's triangle route simply because an older batman is less likely to be put in that position than a younger one.