Some thoughts on it:
7 hours is a long trip for a two day weekend and you would probably find yourself not doing that a lot once the newness wore off. For a 3 day weekend not all that bad in my book..so if you get a lot of 3 day weekends maybe it is feasable.
Not sure if you are fishing trail tourneys out of the dam, Moor's and Kuttawa or opens. If you are fishing open's, you will find plenty of them going out of Paris...some trail tourneys too so you might consider fishing some of them rather than some of the tourneys farther away.
If you are doing a lot of fun fishing down south (below blood and little river) and launching on the north end to get there then you would save a lot of gas but I would expect you are probably already launching from down in that area.
Have no idea about the upkeep. Would depend a lot I would think on the condition of the cabin and also if the lot has a lot of built in upkeep like grass to be mowed, leaves to be raked etc...
Investment wise if it is a good deal I don't think you can loose any money on it....if the prices around here keep going up like they have the past 5 or 6 years you can't help but make money on it.
If it is a cabin you would not be using real often you might consider renting it out to folks coming down here for a few days or week at a time. That is getting to be a very popular thing down here with a lot of cabins and houses for folks that want to own one here but can't get here real often to use it...that way it pays for itself
Not sure if this helps or not...just some thoughts.