I personally like doing the houses more than twice, but it isn't like I can do them a ton when I only go three nights. I don't find stay and scream to be worth my time/the heat, but we do close out the event every night we go. Last year, there was almost never a line for Darkest Deal. It started as one of our top two houses, and after we went through it so many times (because no line so why not), it ended up in my bottom few houses. It just didn't feel special anymore. So I'm not sure where my cap is for when runs become less special, but I definitely found I have one lol
Also, speaking on the express/no express stuff:
Because we only go three days, FF+express isn't cost effective for us. We do FF to attend for a Sun, Wed, and Thurs, and we do single-night express that Wed. I think even without doing stay and scream, we did around 6-8 houses on Sunday and Thursday last year without express anyways, plus Nightmare Fuel once and time for food/drinks. And we don't tend to get in lines over an hour long (so some of the very popular IPs we may not hit more than 1-2 times). It's always a great time!
Edit: We also do the 6 house unmasking tour Thursday during the day, so we run those houses again Thursday night to see the effects they taught us about in their full glory. We just really love learning how the stuff is done and why, so it's like looking at totally new houses when we go on Thursday