I actually like the multi-vehicle idea. Its how I have always done it. I disagree about every day driving a paid for vehicle is making you money. Because another way to look at it.....if you dont plan on keeping the vehicle til the wheels fall off.....every mile you put on it is costing you money by lowering its value.
I have a dodge 3500 for plowing and pulling and hauling. And drive a 01 saturn for my work car. I commute ~30 miles one way, and saturns are very easy maintenance and fuel efficient. Bought it in 09 with 95k miles for $3k. It now has 195k and had minimal maintenance. I'd say it has more than paid for itself. And my 05 dodge 3500 diesel has 94k miles on it right now. My alternative would be to have that truck and nothing else, and be sitting on a 195k mile truck. I drive the car all I can. The truck gets driven when I need a truck.
Same with the wife. 08 nissan sentra "work" car. bought new and now has 155k miles. Aint worth ~$2500 to trade or sell now. But keeps the miles low on her Ram 1500 hemi, which is only used in the winter, or to haul more than just us and the kids comfortably.
For just commuting back and forth to work, with good road conditions, I think its silly to run the miles up on a nice vehicle. I aint out to impress anyone. I am about getting from point A to point B as efficiently as possible.
But given what you are looking to do, I would have to agree to just keep the truck, save up the $5-$6k and just buy the tacoma outright. But if the Ford isnt really what you "want" for a nice vehicle, then by all means get what you want.