Who's making money and how?

There seem to be a few main types of stock-photo contributors on the microstock sites, and I've been thinking a lot about how each of these types of people go about maximising their ROI (Return on Investment).

I've broken down the types of contributors into a few basic groups, I'm sure I'll be missing something here, but hopefully I've got the basics together.

Who's Competing for Sales?

I've split the market into 4 basic groups: -

1. (Pros) First there are professionals, these will include both individual photographers and agencies, who may or may not already have significant income from their work as journalists, studio artists, or other large-scale professional photography services.
   
   
2. (Stoxers) A group of individuals dedicated to making stock photography their sole (or at least a significant) income stream make up a small but determined sector of contributors to microstock, midstock, and macrostock where possible.
   
   
3. (Lifers) Then a larger group, mostly made up of serious, yet not broadly marketed photographers, who may eek out a living with weddings, family portraits, modelling portfolio shots and the like, who will grab what extra cash they can with 'isolated-on-white' product shots and other such reliable sales.
   
   
4. (Tricklers) Bringing up the rear are the aspirational amateurs who maintain a 'day-job' while spending significant amounts of their off-time taking photographs in places they happen to be going anyway, and steadily look for methods to monetise/monetize any pictures they happen to take with potential market value.
   

Who has the upper hand?

I'm making no allowances for special cases here and just considering the likely averages.

In terms of available resources, both time, and hardware, the first three groups will be dominating, with the tools to take the better quality pictures, and the portfolios to back them up, there will be a little give for these groups, affording each of them some chance to sell good work, often.

For Pros in particular, a reputation can be formed with the big microstock sites which will reward them with better commissions, more repeat sales, and for some, their new uploads will become anticipated by their regular customers.

Pros and Stoxers will be in a good position here, with regular income streams, increased ROI, and a reputation backing them up, higher income streams are likely, however it's easily possible to get stuck with only one or two big sites, all geared with exclusivity deals, and gold-member status.

There's not many downfalls to doing business like this, but if one of the big sites changes their policies, the market you're selling to becomes over-stocked, or you take some time out and stop writing articles every other day, keeping those professional relationships up and running, are you going to start losing income?

Freedom

Lifers and Tricklers get the benefits of freedom. If some work doesn't sell on Fotolia, they can remove their exclusivity and move to CreStock or some such else. Heck, since their main income is not coming from stock photography, they can afford to stop uploading all together and take a break.

It looks like Stoxers are getting the short end of the stick here, they have to work harder on their stock than virtually everyone else they are up against. It has to be bigger, better, cleared, more focussed, must have better keywords, thus higher sales, and they're more at the mercy of changes in policy, hence recent outrages about raised prices and lower commissions on some of the bigger sites.

My Benefit

I'm fortunate in that contributing microstock isn't a large part of my income, though every small penny I earn on microstock is a great bonus. If I want to upgrade to a new dslr next year, it'll be mighty nice if the shots I've taken with this one have paid for the next one.

What's your main benefit? I'm really interested to hear if I've missed something blatantly obvious here, or if I'm right on the money.