The economy is in a current state where they want you to greatly value your inventory. They want you to have to think about what you're using it for, and whether or not it's worth it. If you're upgrading every gun you find you're going to start having less, but if you are only upgrading weapons you like and plan on keeping for the entire year 2 of destiny then you should be okay. Personally I've gone up in weapons parts by 500 since TTK came out. But I didn't upgrade anything until I got a great legendary scout that I still use.