I have numerous clients still running amanda 2.4.x clients and talking to my
2.6.1 server.  I would think that maintaining backward compatibility within
the amanda server is a more fruitful path than trying to build the latest
version on all sorts of older platforms.  Is there reason to believe that
older clients will become unsupported sometime soon?

No, compatibility with older client is a priority.

Have you tried restoring? I have a contractor whose assignment is to prove
that we can estore on evey machine in the backup system. She assures me
that earlier cliets cannot do this, and that we must move foward. I have 2
reasons to beleive her. 1. I trust her, and have worked with her for years.
2. It's a fixed price job for here, and the answer she came up will
definatley cost her money.

Jean-Louis