My present bike is an '86 that came with Shimano 600 components. I'm thinking of upgrading to newer or at least cleaner, less-used parts, but I can't afford a brand-new Ultegra group. I might be able to find lightly-used or NOS Ultegra components from the mid-late 90's for similar cost to today's Tiagra. I've enjoyed two bikes, now, with 600/Ultegra groups and they seem to function precisely and reliably.
How does today's "Tiagra" compare with older, higher-end Shimano components?