Just back after a month in Colombia so as its being discussed in this thread, thought I'd offer my two cents. As regards personal security, there is a problem but its nothing like the reputation that has been built up from times past. The Colombian Tourist Boards slogan sums it up well ('the only risk is not wanting to leave'!).
I was in rural areas where it was safe as houses. During the day it was safe as houses virtually everywhere although I have heard of people getting robbed in broad daylight. Night time is a different story. You have to be switched on. Cali is trouble. Medellin and Bogota - were ok, but there were areas where I was told by the locals to get out of as it was only a matter of time before someone pulled a blade on me.
As regards the political problem, there were 25 FARC and 7 police killed in an ambush whilst I was there. However, the government have really turned the tables on FARC and their activity is minimal now.
Having said all that, we are not talking about someone going on holidays. The OP sounds well traveled and if so, probably has developed street smarts at this stage. There are plenty of gringos doing what he proposes in Colombia without any of these types of problems.
I agree with others in that Colombia is a rough diamond with the potential to flourish with regard to tourism. Ironically, they have some great tourist attractions and do stuff like museums and parks well - but their tourist industry seems to be internal for the most part. I have never seen a country with so many police/soldiers/private security - they are really making an effort to make the place safe. Flights are cheap from places like Miami & Texas - and considering that Colombia is probably the only pro-american country in South America, I think you would find a lot of yanks down there if things got just a little bit safer.
I have always had admiration for people that are doing what the OP proposes - takes balls. Not getting ripped off in business dealings has got to be one of the major issues in these countries. Wasn't there long enough to work out how bad it is on the corruption front. However, did come across a european who had a good way of getting around the red tape. He has established a 'boutique' hotel in an old colonial house. Its not registered as a hotel with the authorities so he doesnt have to worry about backhanders and red tape (although as it develops, he says that ultimately he will). Keeps adding rooms as the money comes in. All bookings are coming via the net.