Hi, there. I'm happy to give my two cents on this issue.

Whether it is worthwhile to do the OG a second time really depends on two things
(a) how long ago you did them the first time, and
(b) how well you will remember them . . . and their solutions

The purpose of practice question is to create that "in the test" experience of --- BAM! here's a question asking about a concept in a way that I've never seen before; can I figure it out on the spot, right now?

If you remember the questions well enough that you remember the "trick", the right approach, to solving them, then in a way, that defeats the purpose. It might still be somewhat useful to make sure you remember those skills, but you are not going to get the same benefit.

You mentioned that you are not rushing until your GMAT ---- if you can put several months between the first time you do the OG problems and the second time, that will lower the chances that you remember enough of them to detract from the experience of doing them again.

I would definitely say: any practice test you have, especially CATs, save those for when you want to practice with rigorous test-like conditions.

It's true, there are not that many practice questions out there, but there are a variety of GMAT prep books (none as high as the quality of MGMAT, but good sources of practice questions nonetheless). Also, a Google search for GMAT questions turns up a bewildering array --- some fee-for-prep companies offer a number of free sample question, and there are also just free collections of sample questions. I know sometime folks post collections here and at Gmat Club. Be persistent: there are always more questions.

For free, here's a practice RC question:
https://gmat.magoosh.com/questions/1197
When you submit your answer to that question, the complete video explanation will appear on the next page. Magoosh has over 800 practice questions, each with it's own video explanation ---- a particularly inexpensive source of a whole new batch of questions.

I hope this helps answer you question.

Mike