Warmer temps can also create fusel alcohols...lovely hangover juice. There are many different thoughts on the process and no one is to say one is right...one practice that works for me may not work for another and there are practices I stay away from that make wonderful beer for some of my colleagues.
I go against the grain because I tend to ferment my belgians on the low side (60s, sometimes going in the low 70s at the end of fermentation.) This gives you all the belgian character, but makes for a very smooth, refreshing beer. No wild, crazy esters, but still all the character you need.
In any case, I'd say extract is definitely part of the problem and, believeinsteve, you are almost at 70% attenuation, so it may just be done. How does it taste?
Anyway, in my experience, Conroe, a low pitching temperature won't negatively affect your yeast, as I pitch EVERYTHING in the 60s and ferment there as well. And I have made dozens of fantastic belgian beers.