My decals were coming of my 2006 Allegro Open Road.  They were especially bad on my passenger side cargo lids.  As a master of incrementalism, I removed the old decals with a hair dryer.  You just get it started and then you pull with the hair dryer behind your work.
I then cleaned all the dirt and glue off with iso alcohol using rubber gloves and a rag.  I used frog tape where the old lines of the decal were and masked the other 12 to 18 inches with blue tape and newspapers.  
Here is the best part.  I repainted the old area of the decals with Rust-Oleum Universal Forged Hammer Paint and Primer, Burnished Amber.
It almost exactly matches the color and texture of the old decals. I bought the paint at Home Depot for about $8.00.  The clerk warned me of the 30 minute to 2 hour recoating time or 7 DAYS, which is in the fine print.  I will be doing more of this as the decals fall off.  I think this is much better than new decals, and it costs very little.  This project turned out great.