Yup. That's what toys are for.
My daughter really isn't old enough for cooperative play yet.
My daughter isn't allowed to touch any of my Transformers without my direct permission and supervision except for my PlaySkool and Plush Transformers. One of my former colleagues had an interesting policy with her boys -- never play with a toy that's older than you are.
To me, what's the point of collecting toys if I'm not going to play with them? Just as I collect books to read and food to eat, I collect toys to play.
And it's not as if I made a conscious decision to play with toys as an adult -- I've just never stopped playing with my toys since I was a kid. I started playing with and collecting Transformers in 1984 and I've been continually doing so ever since -- and I have no intention of stopping any time soon.
My play pattern has changed since I first started though -- during the 1980s it was all just action driven ("Let's fight!"); by the 1990s it changed to becoming more story and character driven; by time I was in senior high school I started playing out entire story arc-campaigns that would last weeks, sometimes even months! There was one time when I spent over a year playing out a single campaign (ahh, when I was young and had more free time).
Nowadays it's more or less still the same thing, only that my campaigns are shorter because I don't have as much time as I used to. Depending on how much time I have, I might revert back to just action-packed play campaigns (Michael Bay'd!), but if I have a bit more time, then I'll try to make it more character/story driven. This usually happens when I'm on holidays.
If I ever lost interest in playing with my Transformers, I'd sell 'em. Thankfully that's never happened and I don't imagine it ever will. I've stopped playing with some other toylines (mostly because I have little spare time to play with toys, and whenever I do get the time I almost always choose Transformers) -- and I have sold a lot of those toys that I don't play with anymore. Others I've clung onto, but I'm thinking about selling in the near future. I've never thought about selling off my Transformers collection.