I have lost count of the number of Lego sets that we have purchased for my child and nephews over the last many years.
But as I said in one of my earlier notes, using these sets has helped in instilling a sense of discipline among the kids at home.
The various things that we do to ensure that all sets are usable over a longer period are as under:

1. The best thing is to let your child assemble all the sets and display them in a location within the home that will provide your child the sense of accomplishment ("I have done that!"or "That is my creation!").
   Imagine you have visitors at home and they gaga over the displays created by your child - you can feel the sense of pride swelling in your child.
   
2. Sometimes, there may not be enough space in the home; in such cases what we have done is to disassemble the set and put the parts back into the original boxes along with the instruction sets.
   I can recall these sets being opened during the vacation, and being reassembled after a few years.
   
3. Ensure that the motors are kept along with the respective sets; but please ensure that the battery is not attached to the motor terminals; we have had an instance when one of the batteries was not removed from the motor and over a period of a few months started leaking damaging the terminals.
   I did a bit of soldering to set it right after a bit of snipping and rewiring, but this situation is perfectly avoidable with a little care.
   
4. Donate - over the last many years, we have donated or handed down sets to kids much younger than ours.
   We have ensured that the sets are complete with the documentation and instruction set in place so that the child who receives the set does not feel bad because some of the parts are missing.
   
5. Sell - You can sell the products back on eBay or any of the other website to recover your money.
   Assuming you have spent USD300 on a particular set and your child has used it for say 1-2 years, you can still easily find a buyer for 100-150 dollars.
   Please do ensure that the set is complete in all respects and that no parts are missing.
   If they are missing please do inform the possible buyer to avoid any misunderstanding.