Replying to Ski boot shell-life

Alright, I've been riding the same boots (nordica superchargers) for about 3 years and the liner is really packed out. I've been looking around for new boots but haven't found anything that fits my foot right, so I started thinking about getting intuition liners and insert them in. It sounds like a great idea to save money and what not..

My concern is; whether the boot shell will support me well enough for a couple more years.
How long do ski boot shells generally last?