30 year old house

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I'm hoping to buy a 30 year old slump block house to live in a few years, then sell. Assuming it has been taken reasonable care of the last 30 years, what should I expect to have to upgrade as far as major components? I've budgeted to re-roof in a few years or so.
Will the plumbing and electrical be so out of date that they should be upgraded now, or be a problem to sell in 5-10 years? What else do I need to consider?
Thanks.