In ours game cloisters are also not often used. Most of my fellow players use them to complete road. I like to use cloisters to gain points near my structures, and extend farms. The ffff cloister is for my like a blessing
usualy I can build farm with 10 or more cities if I add such cloister to my farm.
Interesting is that when You play with house rules You lose some control of what tiles are placed near cloister, and cloisters will be completed much faster, especialy when one tile is missing. I will try it in future games. I play a varinat of challenged cloisters and don't know yet how would thuse rules affect my variant.
Another interesting thing is that I teach to play Carcassonne nephew of my wife. 11 years old boy is starting to play like I do
. One of ours recent games ended with score 154 points to 146 points with base game and two exps. Not so large game, but I was schocked that he could adapt my strategies to create a mirror copy of my side of board. Clever boy. Still, back to topic, we play cloisters in a specific way. We tend to do farms of cloisters or to put them in places where there are gap in a city complex, so roads will match. Max three tiles needed to complete a cloister, and thouse tiles are needed to complete roads, cities or extend farms. So it a side building a cloister. Other players, much older tend to not use cloister, and concentrate on stealing cities, or building cities. They do not use cloisters to gain points, and rather than they just use them to compete roads, or fill a gap in board, and sink one meeple.
I was thinking about how to make cloisters more interesting, and I have an idea, but for time beeing will not tell you guys :P I will tell you that one idea is presented in my expansion in work, and another idea is an expansion/variant (don't know how to do it).