Familiarity doesn't really come into play at all past the first couple times, in my opinion.
After the first two, maybe three times, you take a drug, you are familiarized with it (assuming you are taking the same pure dosage). You are already familiar with what it does to you, and the "wow" factor of trying ecstasy for the first few times is largely diminished.
After that initial period, the wow factor is gone, and you are in line with most habitual ecstasy users.
The only other thing that distinguishes you from other users in your experience of MDMA is the level of tolerance (assuming all other things like set, setting, diet, weight, etc. are all held constant).
I don't really understand what you are getting at with familiarity. Do you really think the 12th time is more potent in your mind than the 13th time because you are more familiar with what the drug does to you?
I think the real issue is, after years of rolling, it's hard to find new stuff to do, and even ecstasy can't remedy the fact that you've been doing the same thing time after time.