It depends on what you want to do with your A2000 brian?
If you just want to play all the old games and public domain software, stay with the 2.1 ROM and OS and you will be able to run most things. Some older games were broken with the move to version 2 of the ROMs and OS and only work on OS1.3, or for an even fewer, they require OS1.2 or earlier.
If you want to see what the latest and greatest version of the AmigaOS3.9 looks like, I suggest you get a good graphics card and the fastest CPU with the most RAM you can get, but at least 32mb RAM.
Otherwise, with your current 030, 2mb Chip & 16mb Fast RAM, I would stay with AmigaOS2.1, or move up to 3.1 and get a ROM switcher with a 1.3 Kickstart ROM to play the older games.
You could also softkick into what ever ROM you want if you have the files and your MMU is supported.