I think this topic will be argued and will create many opinions regarding it. But, until there is an ultimate authority on what is or isn't internal power, because it is a subjective term, it will be a term of debate. It will be right up there with all similar debates of religion and God.
Can't fully agree with you on this one Buck. There will never be an ultimate authority on what is or isn't internal power. As you say it is a subjective term, and as such it would be like asking for an ultimate authority on 'happiness'. However it is a real phenomenon and due to its very nature, difficult to quantify ones level of skill via text. The only true measure is hands on with another person.
I also see it as anologue rather than digital, in that internal strength skills can be measured on a sliding scale rather than, you either have them or you don't.
The religion/god debate is different, religion is analogue, you can be a little bit or a lot religious. God is digital, he/she/it either is or isn't and so far their is no proof either way!
The thing is, what are we going to do with these skills if we are fortunate enough to aquire them to some degree. Go round berating those that don't have the same skill level? We'd then end up like missionaries bringing the 'real god' to the heathens.
If having these skills does not improve our overall positive contibution to the wider world, then they are not worth having and in that sense, exactly like religion.
For me, internal strength is a core aspect of aiki, without it aiki is unlikely at best. It should be an integral part of all aikido practice. I also know from my own experience that the main component of aiki is 'mind', however, that mind aspect is totally dependant on the correct state of the body (correct posture, alignment, balance, weight distribution, relaxation, etc.). The mental side allows me to engage with a partner before physical contact, to redirect their energy, to upset their intent in some way, to some degree.
Anyway, I might be talking a load of old nonsense as I have not been 'vetted' by any external authorities yet
. I may well be deluding myself and my students with what I teach them and with what I get from my teachers. However I am happy, they are happy, and my teacher seems pleased with my progress, so hey ho, back to practice I go...