>> Compression testing would be way down on my list as you don't mention that it is hard starting.

Yes, ... and no. If there are 2 or 3 good cylinders with good working glow plugs, the engine will probably start without too much aggro, but still run like a donkey.

The specific problem I'm thinking of is inlet valve seat recession, which, as per Wingas's recent OM606 thread, can give you good compressions on some cylinders, and bad compressions on others.

If the injectors are coming out anyway, it's a perfect opportunity to do a compression test. It's not expensive at this point, with the injectors out, as you've already done most of the prep work.