yeah, but good gameplay and graphics is still better than good gameplay and bad graphics :)
The problem with this idea is that sometimes an upgrade in graphics, particularly from 2d to 3d, requires an upgrade in gameplay. If you just slap fancy graphics on the game, you essentially ruin the origional gameplay, because all the details of pixel to pixel speed and collision detection go out the window. Dev will then rarely spend any time getting those things optimal for the new engine and as a result, you wind up with Frogger on the psx, or worse, you wind up with a game that feels nothing at all like it should. And then It might as well be a whole new game.
Graphical detail isn't part of gameplay, but the fine tuning of the gameplay can be set off balance by changing large aspects of the graphics. Not only that, but games today require a lot more depth in the mechanics to pull off a convincing sense of suspension of disbelief. 2d low rez sprites worked well because your mind fills in the blanks, thusly creating details that aren't there, or even emotion in a 4 frame animation that shouldn't be possible. The more high rez the graphics, the more you have to animate and the more variance in animations you need to portray the same level of realism.
Look at the change from Final Fantasy 6 to 7, and how the emotional context of the characters in 6 were just as deep as in 7, while 6 had essentially 5 'poses' jumping, standing, kneeling, looking down, and dead. Where as final fantasy 7 had a wide range of character animations, from subtle details with hand movements and facial contortions, to bends and rude gestures.
And then from 7 to 8, where again the detail grew and again the number of animations grew, but the emotional context of the characters had begun to decline even more.
As you take things away from the imagination, you have to validate them more to be convincing. Which is why, when you upgrade a game like this, you need to overhaul some its parts. Esspecially the animations and variety of players.
If you only have 1 model per team, 1 set of animations that are basic movements, run, walk, kick, and so on, you are going to end up with a game that feels shallow and bland. It will lack the charm and the presense of the lower rez game, because you will be asked to believe that the players are doing things you -could- see but are not, where as in a low rez game, you imagine they are doing things that you -couldn't- see because your brain is in fill-in-the-blanks mode.