You say 70 C is a little higher than normal, that looks a bit low to me, my one runs at 86 C to 88 C, that's a measurement done on a lap top through the OBD port (the dash gauge reads very slightly lower). As a comparison my oil gauge goes between half and the next segment up when cold and half and the next segment down when hot. When on the move, 2000 - 3000 revs, the gauge stays in the middle and doesn't move.
Oil is thicker when cold and won't pass out the bearings as easily which gives you a higher oil pressure, that is what the pressure relief valve in the pump is for. The oil level doesn't have any affect the oil pressure, as long as the dip tube is submerged into the sump of oil or it's not overfilled and getting foamed up by the crankshaft.
If your oil filter is blocked to the extent that it's affecting the pressure (which seems unlikely unless its never been changed in its life), then I don't hold out too much hope for the engine. Try changing the filter only, they're only a few pounds and easy to do and that will be one item eliminated.
One other thing, what oil do you put in it? I use Castrol Magnatec 5W-30 A3/B4 Fully Synthetic in mine. I change the oil every 12,000 and just the filter every 6,000.
