you will never level-up from stealing 200 by drop-down stealing.  that is the limit the game has.  after that, the only way to increase your stealing skill is by stealing from other players, and yes, that takes a long time.  (ok, so it does increase when you get a counter-steal, but that's rare).
as for the experience, it has been posted on the forum before.  as soon as you get to stealing lvl 200, the exp points you get from drop-down stealing becomes only (approx) 25% of the exp you would get if you stayed on lvl 199 stealing (which is the reason many, if not most, people leave nail-thieves on stealing lvl 199).
--jason

Thats great Jason.  I've got a hand like a crab now but my bank balance looks good for a change.

This is probably a question that has an obvious answer so I'll apologize in advance for asking it.

How do people keep a nail-thief at level 199 without... not stealing?

you dont buy the upgrade from the casino

Of course! :p

>>How do people keep a nail-thief at level 199 without... not stealing?

>you dont buy the upgrade from the casino 

... and deal with / ignore the (slightly annoying) bold message that pops up every successful steal, telling you that you can go to the casino to upgrade your stealing skill.

--jason

Hey there peeps a similar question for the top robbers, since I am robbing 250 and will be clicking like mad once I get to lvl 300 I know you don't gain percentage after that unless you make a successful rob. But does your experience decrease as it does with stealing? I hope not lol it takes ages to level up as it is:-p
Thanks for any help:)
Katie

>once I get to lvl 300 I know you don't gain percentage after that unless you make a successful rob
i didn't think i'd ever heard it before.  so i confirmed today in chat with someone over robbing lvl 300, and it's not true.  you still gain robbing percentage after lvl 300 from trainer houses.

>But does your experience decrease as it does with stealing?
same answer... this is also not true.  there is no cap to robbing lvl's when it gets harder (in the same way that at lvl 200 stealing, there are 2 disadvantages).

--jason