@Turjan - I don't know how the 'attractiveness' thing works between Sims. I always thought it was traits and personal relationships based on one-on-one interactions and actual time spent together. It wasn't until a simple makeover threw my game out of whack did I begin to consider that physical features may play an 'unknown' part in how one Sim view another in some form. If this is written into the game then it would have to be a part of the core game mechanics.
With my other Sim, it wasn't until I cleaned him up (so to speak) did other Sims begin to find him attractive and I didn't change anything about him other than his hair and goatee, his face is exactly the same. Now-a-days when I play his household, he doesn't visit the gym regularly and the female response is just as strong as ever towards him. If slider position plays a factor, then he should have had the same result as before because I didn't alter him.