If you want the paint job to be seamless and have all the color match then yes so the new trunk paint can fade into the quarter panel to insure that it does not look like there are two different colors which would happen if only trunk was painted.
Even if it is the same color the sun and other elements change the color so your trunk might look a deeper more rich color then the .25 panels.
I had a dent on my pass door and had to do the rear door also since it was near the front door to insure a even paint job.
You can see the effect mainly on lips and stuff when people dont blend paint to the car is one white and there lip kit is supposed to be the same white but is off a little.
It really depends on if you wanna spend the xtra $$$ but its worth it.
yeah its really all about the faded paint.. if your paint is in really really good shape, and if your paint man is really really good and matches the (original) color perfectly, you should be able to get away without a blend.
the problem arises in matching the original paint perfectly, b/c the factory uses several different 'tints' over the production run of the vehicle, so even if your paint man perfectly matches the paint code, theres almost no real guarantee that the tint will be perfect. i've seen expensive paint jobs done two or three times with different tints to get just the right color..
sorry! fork up the money!