I somewhat find it hard to believe we are even having this discussion. NOT using a GPS does, IMHO, border on madness. That the use is apparently not even taught in the JAR CPL syllabus simply beggars belief
For crying out loud - use everything at your disposal for a safe flight!
Re the 'club plane' scenario, there is a simple and effective way around this: buy your own portable unit, get really familiar with it and use the installed one as backup.
The above of course only works if the installed one is not one of the fancy 'all functions in one box' models, a la GNS 430. In which case there are free CDs to use at home for training. I sometimes (very rarely) fly a GNS430 equipped a/c and always do half an hour or so with the sim before the flight until I get back into the swing, so to speak.