Depends how much your time is worth to you?

It depends on your results. Some of the agencies in the low earners section aren't really low earners.

I'm really suprised by how different accounts of earnings are on these smaller sites. You never know what will work for your portfolio till you try.

I see, interesting anyway... The idea was something like that: if I have today two hours, should I make an illustrations and upload to all stock agencies, including low-earners or should I rather make 3 illustrations and upload them only to the first top agencies? To be or not to be? 

It is really really important to get your images keyworded in the IPTC data.
When first the pics are ready you can always upload a bunch here and there overnight and then is not really much time you spend.
I use to test the agencies with 30-40 average well selling pictures from different genres. But not the best pictures i have. Im very carefull where they go.

If the test uploads sell to a reasonable degree, I take the time and give them a few hundred more.
Then I forget.

After a couple of weeks I probably remember and check the site, and if im bored enough, I sit and fix captions and press buttons or eventually delete the whole batch.

Else I let my pics sit and gather pennies, and try to remember to get the money down, if there is any.
If an agency annoys me I might actively delete my port and profile there.

If you have 500 or less, good images that sell regularly on the top sites, no.

Roughly you'll make 1/10th of what you do now on SS (according to the chart on the right) from all the sites under the top seven.

You can expect to earn 25% and down compared to what you make on FT.

Example, you make $25 a month on FT, you might make $6 a month, and down, on the low earners.

We don't know who responds to the survey? I assume it's the same as the active people here on the forum, which after a few samples and forum surveys, represent The Top 5% of all Microstock  contributors. The people here are the cream of the industry and represent the top performers. Many have 3000 - 5000 top quality images.

For anyone who considers this, the answer is above. Always imbed the metadata in all your photos. It's much easier since the time consuming work is done. Also images that are refused by the top four are often accepted at the rest. Acceptance and sales, are not a direct correlation to profits.

Best person to answer that would be someone with The Bridge to BigStock, who has virtually all the same images on both. And they can tell us if BS is consistent 13% of SS? That would be interesting to know.

I personally don't spend time on the low earners. I think they are parasites, they lower the value of our images and take away from the top of the market. I'm sure there are others who disagree and feel that competing with their own sales, and making $50 a year doing it, is worthwhile? The low earners compete with the rest of the market based on price and nothing else. They offer the same images that everyone else above them offer, what else can they claim to bring in customers?

I see, interesting anyway... The idea was something like that: if I have today two hours, should I make an illustrations and upload to all stock agencies, including low-earners or should I rather make 3 illustrations and upload them only to the first top agencies? To be or not to be? 

I think it is always better to create first and upload later. However, if you dont suck it up and upload fairly frequently it doesnt matter how many images you have.  As far as low earners I uploaded the same 100 vectors  to all of the sites and tracked the results. After about two months it became real easy to see which sites worked best for my port. Every port is different but my results do not match the table at the right very closely at all.

If you have a large enough portfolio and a low-performing microstock site gets you $50 a month, then 4 such sites will get you $200 a month.

Choose the sites that require little effort to upload and publish.

I think I have a very LCV port. Some good points were made here. And to me it seems true. My port on SS is not roaring with 225 dls per month.
 and so the low earners only get me 6-10 downloads per month. Middel tier about 25 dls per month
But I am shooting what I like and not really stock orientated.

At the moment:
SS 380 photos - 225 dls month
FT 250 photos - 25 dls month
CanStockPhoto 430 photos - 6 dls month
DP 490 photos - 8 dls month
123 460 photos - 25 dls month

if I have today two hours, should I make an illustrations and upload to all stock agencies, including low-earners or should I rather make 3 illustrations and upload them only to the first top agencies?

For photos, I'd say: why choose if you can have both? Just use Lightburner and avoid sites without FTP and with categories, and you can upload to all sites at once.

For vectors, the upload is probably a bit more difficult.

...For vectors, the upload is probably a bit more difficult.

Yes and no. Some sites make it almost as easy to upload vectors as it is to upload photos.

The big difference when it comes to middle and low tier sites is that, going based on the MSG poll, vector artists need to keep in mind that the poll results are probably heavily influenced by photographer results. There are sites that do far better (or far worse) for vector folks than for photographers, so doing a little more of your own trial and experimentation with lower tier sites is necessary if you work with vectors.

For example, my #2 earner last month behind SS was GraphicRiver. GR is barely a blip on the radar in the poll results. So if I only chose sites to work with based on the poll, I'd be missing out on some good earners.

I'd say no, I stopped ULing to the non top 4 sites after a few months. Not only you're wasting your time, but also support agencies that compete only with the lowest prices and lead the race to the bottom. And that is bad for all of us. They also never earned me more than 10-15% and I'm talking about 10 agencies or so, not just a couple. Besides most of those agencies put your files on dozens of partner sites, you can't even track where your content sells and there is often a problem with deleting those files. OTOH FT do that as well.

I'm glad I didn't follow this advice^^.  I have seen my income at two of the top 4 agencies drop by more that 50% in the past year, thanks to search engine changes that penalize top selling (read expensive) contributors.  Thank goodness I am on some of those "low sellers" because they are the only thing keeping my numbers to a tolerable level.