I hear you and I'm a physical kind of guy.
The trade in is a huge negative to digital and I've used that argument too but do you know how many games over my 30+ years of gaming nice traded in?
That's right none, i tend to hoard things until they don't work regardless of their value. It's a failure if mine I know
Edit: bugger, bloody iPhone 3G spellcheck
Depends on the game really, some I keep if I know I might come back to them, but most I know I won't. For example FIFA, you know there will be another out every year