Donkeypuncher pretty much said what I had in mind.
I've always found it cool when my g/f would have a dildo and experiment with it- the thought of her playing with it was always a major turnon for me. Usually she'd be full of ideas when we got together again.
And playing together is even more fun
Besides, it's a piece of plastic. Imagine if you had a rubber vagina, think you'd still want her?