A practical suggestion
I think we've seen both sides of the argument here (and in the other threads on this subject), so can I offer a practical suggestion which helped me in the early days.
Buy a GPS, then plan your trips in threes - whether it be three legs to the same trip or three consecutive trips. Plan and plog the whole thing as if you are going to fly it using map and compass only, then fly leg 1: purely map and compass, with a switched on and programmed GPS on board which is either covered up or positioned so you can't see it (so it can record the leg for future reference); leg 2: VOR / NDB / DME primary while following the map, with GPS as for leg 1; leg 3 GPS primary with finger on map and VOR/NDB info as a backup. That way you keep your VFR nav (which you will most definitely need for CPL nav) up to date, get some practice in on "traditional" instrument flying and get up to speed with GPS. The GPS return will tell you how well you did on legs 1 and 2 and the VOR/NDB will tell you as you go whether the GPS is playing fairly or not. And if leg 1 or 2 goes south, use the GPS to put you back on track, then keep going.