I've thought about 'kicking the habit' a few times, and selling most of the collection off while just keeping a few favourite items. I've actually managed to acquire a lot of the TFs I want already, so the collecting has slowed right down over the past year to year-and-a-half-odd. Japan's good like that.
Then I'd look through my packed-away-due-to-lack-of-display-space assorted TFs (most of them are in boxes in Tasmania, most of the rest are in boxes here in Osaka) to see which ones I'd want to keep, and I'd come across some I'd forgotten I had, and/or others that I'd forgotten how they were actually pretty fun to mess around with or how the design was actually pretty clever, and realise that it's less that I'm 'over' TFs than that I'm just too busy with work to have the time and energy to really enjoy them - my priorities are mostly about teaching my students and daily life stuff these days. I have 3-odd boxes of TFs I've yet to open and/or mess around with (I buy most of my TFs second hand, often loose) and some of them have been sitting there for well over a year. I actually don't open them or get them out and transform them very often, but sometimes I'll just be in the mood to see how a 'new' TF works, or to fool around with an 'old' TF, and that's when it's still 'worth it' to me.
So, for me the time to move on from TFs is when I'm not getting any (or just sufficient) enjoyment out of them anymore. Like most of us here I'd sell them off without hesitation if I needed to raise funds for something more important - they're just toys after all - but that's not the case at present and they're still an enjoyable hobby for me.