21 mpg is better than 32 mpg if that 32 mpg comes with required modifications to the stock drivetrain to make the vehicle reliable
Thou dost have a point. When a diesel newbie asks me about buying a CRD, I give him the following advice - if it's going to be just a weekend vehicle, such that it won't be a major inconvenience if it's down with this or that problem if you leave it bone stock, then whatever floats your boat. But if it's going to be a primary vehicle and will affect your job and livelihood if it's down for any reason, then you best be ready to put around 3 grand into it AFTER the purchase price to make it reliable, if the PO left it bone stock.
Disclaimer - I'm talking only about the 05 and 06 U.S. versions.
OTOH, my old 87 MB 300D turbo cost me 6 grand used, didn't require any mods - just replacement of original worn out parts, and on the one round trip to Texas before it was t-boned easily hit in the 30 to 35 mpg range - with an old style four speed slushbox.