You should definitely go through your old cards. Most aren't worth much but some are worth thousands. Boosters are $9 up here in Nunavut, not sure what their prices are in the real world.
One of the disappointing things to me about current Pokemon TCG is the breakneck speed at which they release new cards, it makes collecting a whole set nigh on impossible without spending a few thousand in booster boxes in a very short window.
Luckily we want the cards to play the game and will eventually spread the other, less expensive cards to our young family members as they age-into pokemon.