The first 3 or 4 numerical characters in the S/N is usually the year and
week of manufacture.
As an example a Sun Fire 280R with S/N 142C061A would have been made on the
42nd week of 2001.

I don't see any reason to start chucking systems as soon as they hit a
certain age.
However, if you're doing server consolidation to replace several less power
servers with a single machine that is always a good move.

Your:

Sun Fire V210
Sun Fire 280R
Sun Fire V480
Sun Fire V880

are all USIII and still good servers.
The Sun Fire V210 is still a currently sold product.
The rest have been EOL for not too long, but far from EOSL.

The other systems like the Ultra class machines are all EOL and if not EOSL
getting close to it in the next year or two.

Trinean