Re: Re-working existing beds
If you want to refresh the soil as well, just used a good well broken down mulch at least once a year. Read the mulch faqs for more details on what type of mulch I mean.
A good mulch will add nutrients and organic matter to the soil. The worms and soil micro-organisms will mix it in for you as it decomposes; no need to move the plants and re-dig.
If the beds have a lot of weeds, put several layers of wet newspaper (easier than cardboard for fitting around closely planted perennials) under the mulch. This will break down after the weeds have been smothered. If the weeds are very bad, you may find that you must dig up a few of the perennials to untangle them, but this is still less work than re-digging the entire bed.