Suggestions for revitalizing hardwood floors without replacing them ??

While a pain, and expensive, full sanding with a rental sander built for that purpose, then refinish.

Since you did not say "laminate" floors I must assume that you have 3/4" T&G hardwood with a site-applied varnish or polyurethane top coat. If I assume that you just have some scratching and wear, there are products like "Scott's Liquid Gold" or several products made by a company called "Bruce" that may bring the floor back enough to make you happy.

Further gone than that, these floors were designed to allow several sandings and refinishings. A deeply damaged floor will need a pro with a drum sander. Last time I refinished I found that Home Depot rented two different less aggressive sanders, one with a large plate that vibrates the various grits of sandpaper and another that uses round discs like an orbital sander. A homeowner would be likely to use one of these sanders and improve the floor greatly with little chance of damage. There are some good water based finishing products for floors out there.

There are companies that do this. Be sure they have a vacuum on the sander or you're in for mucho dust all over everything.

Or you could just clean the floors and add a fresh coat of polyurethane.

You might try painting them. There are so many ways (designs) you could do use. I have seen people paint area rugs on theirs.