That's a harder question, though assuming that your computer has been on for some length of time, 350MB swapped on an 8GB machine isn't something to worry about. (I have about that much on one of my macs right now w/8GB RAM, and that machine has only been using Chrome + normal background tasks since I last restarted it)
If you're looking into getting more performance from that machine, and you are still on a spinning hard drive, I'd research upgrading that to an SSD first - you'll notice a world of difference there. If you're not doing a lot of things at the same time, or you don't experience times on your computer where it occasionally slows down drastically for short periods, then you may not need the additional RAM. (the slow downs tend to be caused by the computer needing to access the disk more frequently when RAM is full or near full)
The other thing I'd recommend, just to be thorough - I'd recommend looking at the Activity Monitor stuff after a couple days of not shutting down or restarting your computer, but during that time you shouldn't check RAM at all. My slight concern here is that if you're reacting to what you're seeing in the Memory tab, you're not getting a complete picture of what your normal usage habits are doing from a RAM perspective. After a couple days, if you check the swap and it's decently large (2+GB, I'm guessing), and you notice slowdowns, then I'd look into possibly upping how much RAM there is in the machine.
