Makes sense that after the got the bugs sorted out that they would try and do what they originally planned. Its also understandable that after the success of the Surveyor landers that such planning would have been shelved.

According to:

http://history.nasa.gov/SP-4210/pages/Cover.htm

Block 4 was to include better imaging and other "non-visual" science (fields and particles), while a briefly considered Block 5 would have included hard-landers.

Phil

There were two reasons why the Ranger series was abandoned after they finally got the Block 3 version to work:

1) Lunar Orbiter and Surveyor were in the works and designed to provide orders of magnitude more data than the Block 4 and Block 5 Rangers could ever provide. It seemed a waste of money to continue to pour it into Ranger when much more capable spacecraft were about to come online.

2) Ranger had a very limited view at high resolutions. The way in which field of view decreased as resolution increased limited the ability to understand fine-scale structures in context with their surroundings. The three Rangers which returned imagery served their designed function of imaging the lunar surface at very high resolution and determining some of its basic properties (slope, cratering, etc.). But additional Rangers would have given very little more data and wouldn't have been all that helpful in studying the Moon.

-the other Doug