Building with Legos

Do you have a child who can't get enough of Legos? If you do, then I need some advice.

Legos promote building,

 and creativity.

Following the instructions included in the kits teaches kids about engineering drawings.

My kids like Legos, but they don't love Legos. 

Once a model is completed, it is displayed for a while.

...... but then what? What do you do with the Legos?

Question 1: To mix, or not to mix???????
If the kit pieces are mixed into a big box full of Legos it will be nearly impossible to put the kit together at a later time because finding the pieces will be difficult. If the pieces are left with the kit, there are lots fewer Legos to use.

Question 2: What are your kids creating with Legos?
The rooster and vehicle below the rooster were created without kit instructions. Mostly my kids create from kit instructions, but I think it would be good for them to design more on their own.

Question 3: Have you found any good books, videos or websites that motivate your kids to create with Legos?

I did a quick web search and found these two posts: 16 Awesome Uses for Legos and Use Legos in Creative Ways for Practical Household Solutions. If I show my son these two sites, we're sure to have a Lego potty.

What has been your experience with Legos?