I was getting something out of my front trunk (frunk) a couple of weeks ago, when the hood fell on its own hitting me in the head. No damage done, but I realized that it must be time to replace the gas struts. I'm not sure when they started losing their pressure, but after I installed the new ones I immediately noticed that they spontaneously raise the hood from about 60% to full open by themselves - I don't think mine had done that for some time, so if yours aren't doing it either, it's probably time to replace them.
Replacing the struts is a very easy DIY fix which can be accomplished in less than 10 minutes. In addition to the replacement struts, all you need is a long, small blade screwdriver, and something (or someone) to hold the hood up while you replace the struts:
I used an extension pole to hold my hood up while I worked on it. The replacement struts (997.511.551.01) are shown below - I ordered them from an online parts supplier which specified ordering specific left and right struts, but as you can see, they are identical. They were about $33 each.
The struts connect by a simple ball and socket joint, held in place by a little metal clip. The close-up below shows the metal clip. Note the groove above the clip - when you are removing the strut, you are basically just pushing the clip up into that groove, which releases it.
The next picture shows the back of the clip, where you insert a small blade screwdriver, and lever the clip up into the groove.
Here's how it looks removing the old strut (starting with the upper connection):
You might have to use the screwdriver to lever the strut socket off of the ball; then repeat for the lower connection. Attaching the new strut is a snap - both literally and figuratively - just push it onto the ball at each connection and it snaps into place (just make sure the gas cylinder is up). Check to make sure the hood is functioning properly - as noted above, it should lift the hood on its own from about half open position.