Good morning Hosamov!
I recently paid about $6/lb for a bulk lot of 27lbs of Lego (total of $160) and it had several old sets in it (the Western theme) along with a bunch of others. I took the chance on it as I saw it had a near complete Fort Legoredo and that alone was worth about $120 used. I purchased the lot with completing and reselling sets in mind. After many, many hours I made about $100 on the deal. At the end of the day, I sold off 3 sets and re-sold the rest on Craigslist @ $4/lb just to be rid of them. Personally, I would not do it again, here is why:
Downsides
It's a lot of work and time
My collection of Lego is almost entire brand new or mint and I plan to keep it to only new bricks I have bought, so the extra parts were not valuable to me for MOC.
These Lego were well played with (eg: dirty, bitten, scruddy - the kid seemed to have a vendetta against minifigure legs)
Counting out a set, then inspecting to root out Megabloks, tooth marks, damaged pieces takes a lot of time
So after hours of work, I now had 3 or 4 sets counted out and a list of missing pieces, next stop BrickLink to try and find them all. I spent hours comparison shopping enormous price differences on some old parts (a rifle was selling for anywhere from $0.10 to $0.95 and I needed about 10 of them). I had to place 3 separate BrickLink orders and still didn't have all the pieces or the patience to complete the set.
Cleaning by hand thousands of Lego is not fun
It's a lot of work and time
Upsides
Found a cool old rocket ship set for my son I wouldn't have known about otherwise (You can buy used and complete on BrickLink for $10 )
Sort of an adventure finding rare pieces and figuring out what sets they go to.
I thought I would enjoy sorting through pieces a lot more than I did and if that's all there was to it, I would probably have been more excited. But trying to turn a profit, I'd say I made less than $5/hour for all my efforts. If you decide to go through with it, I wouldn't offer any more than $5-6 a pound, scrutinize the Lego when you see them for Megabloks, if you see some, no need to turn down the deal, but I would reduce my offer by at least $1 or 2 based on the density of them. Some of the sets in mine were partially assembled and had a thick layer of dust on them, which means you will need to clean for sale or for playing with, so keep that in mind. Looking at the pictures of the manuals and Lego, the Castle and the Indiana Jones are the only sets that might have some decent resale value but they are smaller play sets. On the other hand, they look pretty clean which is a plus. Hope this helps, let me know if you have any other questions about my CL experience.