hmm, I'm not really much use. My Tiagra shifters died (alas, too young!) and I replaced them happily with 105s. If you are happy with SRAM, i'd be inclined to replace the broken components and keep going. But I guess if everything is nearing end-of-life, then complete replacement is in order because it's cheaper than buying piecemeal. I would change them, cause I like Shimano.
@vickster is a fan of SRAM, and would probably upgrade but not change brands.
Edit: my shifter failed after 5000miles. I'd assume the derailleurs had a long life left.