The strength of a poem can be found in the power of the inspiration, and the skill of the poet to capture and convey that message or tell that story is what makes a poem great. Writing is all about the process, if you're passionate about the act of writing poetry, then the skill, editing and technique will follow as you read other poets and apply yourself to hone your craft.
A poem is like a photograph, it's simply a snapshot of a moment in thought. The person taking the photo may understand the mechanics of how a camera works, they may know what buttons to press to achieve the right settings for the desired effects, but the true skill in taking a great shot relies on the instinct in knowing the right angle to achieve that perfect composition, and where to position the sun to give you the right amount of light and contrast. Poetry is everything that happens before you capture that moment.
In regards to the perfect length of a poem, I think the shorter the better, only through choice, because we're becoming increasingly impatient as humans, but there is skill required in both being concise and writing something epic, both need to be compelling.
I agree with that, up to a point. Poetry is taking a snapshot of a moment, but where (in my opinion atleast) it surpasses photography is that you actually describe what's going inside the subject, rather than just capturing what it looks like. Excuse me while I ponce it up for a moment, but for me, photography only shows the exterior, but if your imagery is good enough then poetry shows the exterior and the inner workings. And the moment can be extended with poetry, whereas you only get the split second With photography.
P.s I'm sure if you write something un-put-downable then that short attention span is cured.