Grass is always greener on the other side.
IMO, you won’t look twice at another girl if you’ve really found the one you want to be with. That said, if you don’t know that yet, then perhaps it’s worth a meet with the 2nd girl?
The way I see it is that whilst looks are important (well IMO you have to fancy a girl rotten before you pluck up the courage to ask her out/buy her a drink or whatever), they are essentially the foot in the door to a relationship, just as a good CV is to getting a new job. The CV could be full of great things about you, but if it’s laid out badly, or looks crap, it gets chucked in the bin. The 2nd girl may of course just be a total dud in the personality department too, I have spent many a night eyeing up a girl, working up the bollox to go and chat to her, then when I have done she has had about as much personality as a chair! Of course I have also been pleasantly surprised on a number of times too.