It's been my experience that many older rhodies that have been looking sad for awhile are sitting in some really compact soil. Maybe the soil needs to acidify, maybe the roots dry out in the summertime, maybe the rhodie is iron, nitrogen deficient. Here's what I've done to get those beasts in order:
Prune. Prune after bloom. Cut out the dead, the weak and the weird. Pruning rhodies can be fun if they have a good shape. Make sure, of course, you use sharp shears and make clean cuts.
Fertilize. The soil in early spring should already be pretty soaked, but if it's not make sure you soak the roots. Use a rhodie/camelia fertilizer that will help acidify the soil. If you're an "all organics or bust" type A personality, fine, use organic, but you'll need to use more and more often. If you want to use chemical, fine too, just don't over feed. I don't usually recommend those fertilizer spikes but for older, compacted, larger, neglected shrubs like rhodies they can really help add minerals throughout the growing season. Stick them a little further away from the rhodie than the box recommends. Rhodies have shallow root systems and it's generally best to be conservative with chemical fertilizers. If you notice burning on the leaves that wasn't a problem in the past it may be getting too much.
Bust the soil up a little if it's rock hard. Don't do this too close to the trunk. In general, the lateral leaf growth will tell you where the roots end. Don't go crazy, just hoe it a little so the fertilizer can reach the roots.
Don't let your rhodie dry out. The roots are close to the soil, keep them moist but not wet.
Transplant if possible or necessary. Don't do this if they're too big. Maybe it's getting too much hot afternoon sun. Maybe it's just sick of being in the same place for ten years. Sometimes people forget that transplanting is a possibility. If it doesn't take, then fine. Go out and get a new one. You gave it a try.
Some people treat their plants like they're tender alien beings. I don't. If I'm sick of looking at some scraggly old thing I'm going to either go at it for a season and whip it into shape or rip it out and send it over the cliff. Life's too short to be forced into staring at some ratty, mildewy skimmia. Do it a favor and put it out of its misery if need be.