small bloggers especially the newer ones don’t have enough content to hold on the traffic nor project a certain brand image

I disagree with that – if its a regular blogger, “enough content” can be produced within 1-2 months(assuming (s)he knows the trade). Also, blogging is more about being regular and feeding your readers/subscribers with quality posts.
As regards the ideal time you say, most bloggers do it – I agree.
As for sharing lessons with existing readers, lol

I think for bigger cos spending on advertising is buidling up its brand value to further translate into brand association…

small bloggers especially the newer ones don’t have enough content to hold on the traffic nor project a certain brand image.. they are still in the stage of building up a certain brand value and identity..

of course it can also be noted that havign an advertising budget itself would project a certain image of professionalism.. but like you said sometime the cost of the risk is way too much initially…

in my opinion the ideal time for a blogger to promote and spend on advertising is when he has establsihed a community… it then begins the process of giving not just the blog but the blogs visitors and users an identity which will cover the risk to a great extent.. (if it succeeds you will have mor epeople.. if it doesnt’ you will have some lessons to share with your existing ones..)