Absolutely buy another FM3a - they are wonderful cameras with good features. My black FM3a was bought new and I wouldn't hesitate to buy a chrome one, provided it was in mint condition. Although I use all my cameras, I do keep them in top condition.
The reasons to buy:
- Nikon's last real manual camera (FM10 doesn't count)
- Both aperture priority and manual
- Can use it manually without batteries
- High build quality
- Nice viewfinder display
- They're just fun to use
- Somewhat rare and collectible - they seem special
Yes, an F2 is more of a professional's camera and has two or three more valuable features, but by now they've become common and boring. Can't say F2's are really fun.