One of the best and first upgrades you can do is to replace the plastic charging handle with a metal one. I have been using the Plinker Tactical without issue for years with no damage to the polymer.
I'm an engineer so I look at it a little different perhaps..
I've got over 15k rounds through my 15-22. Still using the plastic charging handle. You use the charging handle around every 25 shots, less if you have no fail to feeds, fail to eject. In fact, during an entire range session, if you're lucky, you may use it only once, if that! I tend to use the charging handle the most after cleaning, cycling the bolt several times.
The trigger, on the other hand, is used every time the weapon goes bang. The stock trigger is a milspec trigger, so at best, it's 'ok'. You can get a good trigger for under $100. Add the Jp yellow springs for a light trigger pull.
Given these criteria, IMHO, one of the best and first upgrades one can do is to put a better fire control group in the rifle. It's about the same cost, improves function and is used every time the weapon is fired.