The B17 is a great choice unless Brooks releases the B17 Imperial rather soon... I got to beta test this saddle and it's as good as a saddle gets.

As far as throwing money at bikes goes... if a part is in good condition and an upgrade won't make things that much better I'd keep it.

I still run a high number of old 3 piece bottom brackets that have seen 1000's upon 1000's of km and are still in beautiful shape and far smoother than many new cartridge bb's.