Ian, I LIKE the new way you're approaching things.
I try to do the same.
Here's a question: In my opinion, there have been a few posts here recently that were plain AWFUL!
What's the right thing to do, in light of the request by the poster to comment?
Russ, I usually respond in a general way if the tune is missing some chords or could be polished up a bit.
If I feel the person posting is really interested in helpful criticism or suggestions on how the music can be made better, I most always Private Message them first and give them a heads up on what I might be posting in regards to their tune.
I ask is it okay for me to post what I've planned on posting.
If it is, then I go ahead and post in the forum...if it isn't, I'll more than likely not post anything.
Not everyone handles criticism well, no matter how constructive or diplomatically worded, and that goes for pros and amateurs alike.
If it is something minor, like a volume/balance issue (voice or lead sound too loud or too soft), I will usually go ahead and post without the above procedure.
For some players here on SZ, this may be their first time posting music on a public forum, so I try not to post in such a way that may discourage them from even trying again and perhaps take away any opportunity for them to get more comfortable with future suggestions and/or criticisms.
If the poster is a seasoned performer or someone who has been playing a long time, I usually PM them first.
I was a Yamaha teacher for quite a few years, and, I learned how poorly worded criticism, especially in front of others (especially their peers), can cause far more harm than good.
Criticism is like castor oil...easy to give, but hard to take, so I feel I best deliver it in the right amount, at the right time, and perhaps with a bit of sweetener to take off the bad taste.
On the other hand, I have a friend who can take several castor oil capsules and chew them up before swallowing.

People like that are rare, probably as rare as those who can handle point-blank criticism.
How am I doing so far?

Ian