Never, ever, ever, never Powerwash pavers! BAD IDEA! If you are like most, you are going to go out there, put a narrow tip on your power washer and have at it thinking you are going to get every speck of dirt off those pavers and make them look brand new. What you are actually going to do is power wash the mortar right out of the pavers and expose the bare aggregate stone the pavers were made with. You essentially are going to age the pavers in a few minutes of what would take years naturally. Either use a surface cleaner head attachment on your power washer or just a scrub brush with a handle and regular old soap. The average front walkway is 265 square feet, or using 6 x 6 pavers right around your estimate of 1000 that you would need to move. I'd do the lift and relay if I were you. The ground has settled about all it is ever going to over 20 years. Fine tune the base, and lay some new pavers. For about $1000 you can have all brand new pavers and improve your property value. Put the old ones on craigslist for free and someone will do the half the work for you.