An easy non-aggressive way to test yours and others level of ability, understanding, and knowledge of Aikido.
Just grab someone's wrist tight and have them perform Irimi Tenkan. If they are able to do this quite easily with no force, without trying to hit or distract you, then they have a good level of knowledge and understanding. If it is difficult, then more work is obviously required.
You can use this small simple test throughout your Aikido journey to gauge yours and others level of improvement (or lack of).
This is also a very good way to assist in finding a good teacher as well, just ask if it is OK first. Any decent teacher will just smile and offer both wrists to you, so you can choose which one to grab.
I strongly believe that the "Secrets of Aikido" are in the basics.
Do not make the mistake of rushing past the basics to try and obtain all those flashy techniques.
If your basics are weak, then so shall your Aikido be.
Enjoy the journey.
although I like the thrust of your post, there is one point I can't agree with and that is the 'grab someones wrist tight' part. It doesn't matter what move is performed, post grab. It is the tightness part I have the issue with. When you grab with tightness, there is tension, where there is tension there is no relaxation. It is just too easy to move someone who is tense. This is quite a complex issue as some styles practice with much more 'force' than others, some go for full resistance and some for full compliance and all points in between.
In my own experience, a uke that uses strength to grab, does not have the required freedom to follow with non resistance in a completely on balance way. It is the lack of sensitivity to every subtle movement that makes them prone to be easily moved.
A uke that holds with relaxation, with their centre in their hand/s, full intent on the objective and a completley free to move body, is a completely different animal than the 'tight grabber'. find one of those to test yourself against, they are very easy to move if the principles of aikido are followed and almost impossible to throw if they are not.
Personally, I think it is a difficult job for a beginner to gauge the level of a teacher. If the teacher has any resonable level of aikido, they should be able to deal with a beginners grip.
Anyway, you are right about the basics needing to be right, I'd much rather spend time looking deep into them than building an arsenal of flashy techniques.
I'm not sure about aikido having 'secrets' though, there are things that some don't know (yet) and there are things that some don't see even if it is there to see, but secrets? who is holding on to them?