I think it would depend on the year for me. If it's 21-speed with trigger shifters I say ride the heck out of it. If it's 18-speed with thumbies I might give it a miss. But even a cheap Giant is a good bike and probably deserves a home if it's not thrashed. Modern equivalent new would cost you $400-600, I think.
And the cost for rack and fenders is the same whether you get a new bike or keep this one.