A lot will come in to play here like stack sizes, ICM, opponent type and so on. I will speak in terms of generality here (if thats possible in poker) and say it is usually a hand that you should value but not over value. It is a hand you should be betting with for value most of the time but if you face a lot of resistance you need to tread lightly. A lot of the spots will probably be bet fold spots unless you are pot committed or are getting excellent
odds to call. I think it also depends on if you are using both your cards to make the flush or just one of your cards. If there is three to a flush on the board and not four then you obviously need to value your Q high flush more. Many players do play Ax suited a lot so you will run into that at times. Your Q or J high flush really goes up in value when you are using both your hole cards and the Ace of the suit is on the board. The ace being out there significantly decreases an opponents chance of having the flush since they cant have the Ax suited.