1. RAM. It looks like you can safely try and add a single second 2GB stick.
https://www.amazon.com/M378B5673EH1-CH9-Samsung-1333mhz-PC3-10600U-Desktop/dp/B00DUG5M0E pegs this at 15 dollars. TO AVOID COMPLICATIONS ALWAYS USE THE SAME MAKE, MODEL FOR ALL STICKS.

2. LSI SoftModem. I wonder if the old dialup modem can be removed. You may need the slot and it does use some memory for the driver.

3. Given the low ram and doubt if any driver updates are ever going to appear. Why not remove Intel Driver Update Utility and Intel's Energy Server items?

4. Same comment for YahooAUService

5. GPU suggestion. I would look at nothing older than say this one:
That's about 60 dollars.