It is very difficult to actually come out financially ahead with 3 vehicles instead of 2. I did decide to go the 3 vehicle route but I knew that when buying my Suburban so I intentionally bought an older one with more miles so I had less money into the tow vehicle. I won't put that many miles per year on it and I will be able to use it for 10+ years. If I were driving it every day I'd have to get rid of it within 7-8 years. I figure I'm just breaking even. It would be cheaper actually to fork over the money for a 2008 2500 Suburban with the 6.0L and 6 speed (versus the 2003 with the 8.1L) and use it for a daily driver and just have 2 cars since it gets much better fuel economy than the 8.1L. I prefer the older Suburbans however as I get the 8.1L, the 3rd row is more comfortable, I was able to upgrade the hitch, etc. I also like the convenience of a 3rd vehicle. I can have it all hooked up and ready to go when I get home from work for weekend trips and both of the other cars are available for going to work that day. It is also nice when I want to work on one of them or take it to the shop for repairs/maintenance, it is rarely a rush as I still have 2 available vehicles. It is more personal preference if you ask me. You have to be VERY careful if you expect to save money. It gets complicated to calculate costs as vehicles will need to be replaced at different intervals, variations in insurance, different fuel economy depending on how the vehicle is used, etc. Regardless, the vehicle I drive every day needs to be something I don't mind driving. I'll gladly drive an older car, but not a beater.
